Implantable lead

ABSTRACT

A highly flexible implantable lead that offers improved flexibility, fatigue life and fatigue and abrasion resistance improved reliability, effective electrode tissue contact with a small diameter and low risk of tissue damage during extraction. In one embodiment the lead is provided with both defibrillation electrodes and pacing/sensing electrodes. For defibrillation/pacing leads, the lead diameter may be as small as six French or smaller. The construction utilizes helically wound conductors. For leads incorporating multiple separate conductors, many of the helically wound conductors are arranged in a multi-filar relationship. Preferably, each conductor is a length of wire that is uninsulated at about the middle of its length to create an electrode, wherein the conductor is folded in half at about the middle of the length to create first and second length segments that constitute parallel conductors.

FIELD OF THE INVENTION

The present invention relates to the field of implantableelectrophysiology leads including cardiac defibrillation and pacingleads, diagnostic leads and neurological stimulation leads.

BACKGROUND OF THE INVENTION

Implantable medical leads are used in a variety of applications toconduct energy (e.g., electrical, photonic, etc.) between energy sourcesand various portions of the body. Diagnostic leads are implanted tomeasure physiological parameters over time, for example blood pressure,or collect and transmit physiological data such as nerve impulses andcardiac rhythm data. Stimulation leads discretely deliver energy totargeted tissues. Neurological stimulation leads are used to block pain,for example. Cardiac stimulation leads are used to deliver low or highvoltage electrical energy to pace or defibrillate the heart.

Transvenous defibrillator leads are used for the correction ofventricular or atrial bradycardia, tachycardia and/or fibrillation.Leads of this type are intravenously positioned, and are used to providea variety of diagnostic, pacing and defibrillation functions. More thanone electrode may be provided if it is desired to provide electrodes fordefibrillation and for pacing and/or sensing. Typical cardiac leads arepositioned into the right atrium and/or the right ventricle. Morerecently developed leads are positioned into the coronary veins of theleft side of the heart for use with cardiac resynchronization therapy(CRT).

Conventional transvenous defibrillator leads use a stranded wire toconduct the electrical energy from the connector at the proximal end ofthe lead to a coiled defibrillation electrode near the distal end. Adiscrete connector or junction is generally used between the conductorand the electrode. The junction may be formed by a connector component,a crimp joint, a weld, or combinations of these. Medical leads withdiscrete connectors may suffer from decreased reliability due toconnector interfaces serving as points of failure. Connectors also tendto increase the diameter of leads, at least in the region of theconnector. This may lead to increased tissue attachment in these regionsand commensurate difficulty in lead extraction (sometimes necessary incases of infection, dislodgement or lead failure).

The electrode surface of an implantable lead is typically exposed,allowing it to contact or be in close proximity to the desired surfaceof the tissues or surrounding fluids. Such exposed electrodes have afundamental disadvantage with tissue ingrowth. The ingrowth andanchoring of tissue into the exposed coil makes the lead difficult toextract and may also adversely affect electrical performance of thelead. Various electrode coverings have been suggested to eliminate orminimize tissue attachment to the electrode. Defibrillation electrodesprovided with coverings of porous polymeric materials includingpolyurethane and polytetrafluoroethylene (hereinafter PTFE) have beendescribed, wherein the penetration of bodily fluids permits electricalconduction through the porous polymer even though the covering itselfmay be electrically non-conductive. Various electrically conductivecoverings such as porous polymeric materials having void spacespartially filled with conductive materials (e.g., carbon) have also beendescribed. These porous coverings may be treated to improve wettabilityand conductivity.

It has generally been desired to manufacture leads with the smallestpossible diameter while providing sufficient electrode area. Othersought after attributes may include isodiametricity, flexibility, flexlife, fatigue resistance, abrasion resistance, corrosion resistance,tensile strength, and minimal tissue ingrowth, all of which contributeto good long-term reliability and extractability with minimal risk oftrauma.

SUMMARY OF THE INVENTION

An implantable lead is described that offers good flexibility, fatigueresistance and flex life, improved reliability, high abrasion, fatigue,and corrosion resistance, high tensile strength and effective electrodetissue contact with a small, isodiametric profile and low risk of tissuedamage during extraction. The lead also offers similar defibrillationimpedances and thresholds, pacing impedances and thresholds, and sensingR-wave amplitudes when compared to commercially available leads. In oneembodiment the lead is provided with both defibrillation electrodes andpacing/sensing electrodes. For defibrillation/pacing leads, the leaddiameter may be as small as six French, five French or even smaller. Thelead may optionally be made to have a smaller diameter for portions thatreside intravascularly (e.g., 5 French) and have a larger diameter inother regions, for example in portions that reside extravascularly(e.g., 6 French), providing even greater abrasion and crush resistanceresulting from greater insulation thickness in those portions. Suchvaried diameters may be created by using the same materials or sets ofmaterials in each region of different diameter. For example, layers of alead may be “built up” to create the larger diameter region. Atransition in diameter may be present between the regions of differingdiameter. Such a transition may take the form of a taper or be moreabrupt.

The construction utilizes helically-wound conductors, each of which ispreferably made of multi-stranded wire. For leads incorporating multipleseparate conductors, many of the helically wound conductors are arrangedin a multi-filar relationship. The insulated portions of theseconductors are preferably provided with a thin, strong fluoropolymerelectrical insulation; a particularly preferred material for thisinsulation is a non-porous ePTFE provided with an adhesive coating ofthermoplastic fluorinated ethylene propylene (FEP), referred tohereinafter as “substantially impermeable ePTFE/FEP insulating tape”.ePTFE (expanded polytetrafluoroethylene) is well known in the medicaldevice arts; it is generally made as described by U.S. Pat. Nos.3,953,566 and 4,187,390 to Gore. The particular tape described herein isslit from a substantially non-porous ePTFE/FEP film having a thicknessof about 0.0064 mm, an isopropyl bubble point of greater than about 0.6MPa, a Gurley No. (permeability) of greater than about 60 (minute/1square inch/100 cc); (or 60 (minute/6.45 square cm/100 cc)), a densityof about 2.15 g/cc and a tensile strength of about 309 MPa in the lengthdirection (i.e., the strongest direction). A 0.0025 mm thickness of thissame type of substantially impermeable ePTFE/FEP films was also used inaspects of the construction of leads of the present invention describedbelow. This thinner film will be referred to hereinafter as “thinnersubstantially impermeable ePTFE/FEP insulating tape”. Other layers offluoropolymer films may be used in addition to the substantiallyimpermeable ePTFE/FEP insulating tape, including porous ePTFE to enhanceadhesion, flexibility or other properties.

“Insulation” is defined herein as a material intended to precludeconduction of electrical charge to adjacent tissue or to adjacentinsulated electrical conductors. Preferably, portions (e.g., lengthportions near the distal ends) of at least some conductors areuninsulated and serve as electrodes or portions thereof. As such, theinsulated portions of these conductors are continuous with theuninsulated electrode portions, thereby avoiding the use of connectorsbetween the conductors and the electrodes. The lack ofconductor-to-electrode connectors enables the construction of anisodiametric lead with high fatigue resistance and tensile strength andenhances reliability.

“Lead body”, for purposes of this description, is the portion of theimplantable lead located between the termination of the conductors inthe proximal connector and the tip assembly, and includes the pacingcoil.

For descriptive purposes, the “proximal end” of the lead is consideredto be the end provided with at least one electrical connector intendedto enable the lead to be connected to a power source or sensing andcontrol system. The “distal end” is the end opposite the proximal endthat is typically affixed to a tissue surface, for example the heart.Figures are designated with arrows labeled “P” (proximal) or “D”(distal) to indicate these respective directions.

In one embodiment for cardiac use, the lead includes four electrodes. Insequence, beginning proximally and moving to the distal end, these arethe proximal defibrillation electrode (typically positioned in thesuperior vena cava following implantation; also referred to as SVCelectrode), the distal defibrillation electrode (typically positioned inthe right ventricle; also referred to as the RV electrode), a sensingelectrode adjacent to the distal tip and a pacing electrode located atthe distal tip of the lead assembly.

The distal tip may be a “passive fixation” design, commonly known in theart, or an active tip including a helical fixation member that may berotated by a practitioner at the proximal end of the lead to drive thehelical fixation member into and anchor the lead in the heart tissue ata chosen location. When the helical fixation member also serves as thepacing electrode, it is often connected to a helically wound electricalconductor (often referred to as a pacing coil) that is centrally locatedin the lead and extends to the proximal electrical connector. Thisconductor serves to provide both a mechanical (rotational) and anelectrical connection to the helical fixation member. This helicallywound electrical conductor contains a hollow lumen that provides aworking channel to allow access for a stylet during implantation and/orextraction. The pacing coil may also include a non-conductive filamentwound into the coil as one of the coil filars to improve MRIcompatibility. Distal lead tips may also include a means for drugdelivery such as a matrix containing elutable therapeutic agents such asanti-inflammatories. Additionally, distal lead tips may include featuresto reduce risk of perforation of the tissues during and afterimplantation. These features may include flange-like features thatincrease the diameter of the distal tip to lower the tendency forperforation to occur. This diameter increase may be achieved through useof shape-memory alloys or polymers, swellable polymers, compliantpolymer or elastomeric features, and dissolvable/bioabsorbablematerials. These features may also include therapeutic agents for drugdelivery.

The electrical conductors providing electrical potential to the otherelectrodes are preferably arranged in a helical winding disposed aroundthe inner helically wound conductor connected to the pacing electrode.The helical winding of these outer conductors is preferably amulti-filar helical arrangement. In one embodiment, the individualelectrical conductors are folded approximately in half to form a 180°bent end that is located distal to the proximal end of the lead, withthe portion adjacent to or adjacent to and including the bent end beinguninsulated and configured to serve as an electrode. The remainingportion of each of the first and second length segments that constitutethe two sides or ‘halves’ of each of the folded conductors is insulatedand extends to the electrical connector located at the proximal end ofthe lead. The two first and second length segments will typically beadjacent to each other in the multi-filar winding of electricalconductors. The provision of the two first and second length segmentsallows for the use of a smaller diameter wire to supply the electrodeand adds to the flexibility of the lead, reduces the lead diameter,improves fatigue resistance, and provides for redundancy in supplyingelectrical potential to the electrode.

Additionally, in the construction of both the pacing coil and thewinding of the conductors in the lead body, the helically wound wiresare constrained in a strained condition. This is accomplished by windingthe wires over the mandrel (for the pacing coil) or lead bodyconstruction (for the remaining conductors) and maintaining the positionand tension in the wires while outer layers are wrapped over thestrained conductors with, for example, the fluoropolymer tapes describedin the manufacturing descriptions and then heated as described. Theheating bonds the fluoropolymer tapes preventing the wires fromexpanding to the relaxed diameter of the wound coils. It is believedthat this method of achieving the desired final lead outside diameterreduces the required strain and stress seen by the wire during use andcan improve fatigue resistance and lead robustness.

Filars are considered herein to be individual wires or filaments (e.g.,individual conductors) within the helical windings of lead conductorsthat make up the lead body. Each of the first and second length segmentsof the folded conductor are considered to be individual filars.Typically, the filars of the first and second length segments of anindividual folded conductor will be placed adjacent to each other in themulti-filar helically wound structure of the lead body.

The two free ends of the first and second length segments (opposite thebent end) will typically both be connected to the same contact on theelectrical connector at the proximal end of the lead. While generallythe two first and second length segments will be of approximately equallength, this is not a requirement.

While it is preferred that the bent end region of the folded conductoris uninsulated and configured to serve as an electrode, in anotherembodiment, the uninsulated portion of the folded conductor is locatedaway from the bent end where the conductor remains insulated. In yetanother embodiment, there may be multiple uninsulated portions alongeither or both of the first and second length segments of the foldedconductor which serve as electrodes. The length of uninsulated portionsmay be varied, as may be the location of uninsulated portions along thelead. Additionally, the current density of the delivered energy may bemodified by using unequal lengths of insulation on the first and secondlength segments of an individual conductor. This results in unequallengths of the uninsulated first and second length portions (theelectrode portions) as well, resulting in a different current densityfrom what would be expected if the lengths were equal.

In another embodiment, the electrode region of the conductors (strippedof the outer, thicker insulation), may then be provided with a verythin, tough insulation, using the previously described substantiallyimpermeable ePTFE/FEP insulating tape. An additional conductor, in theform of a noble metal wire (e.g., platinum iridium) may then be heatedand tightly wound around the stripped and thinly insulated conductors toprovide an electrode that is remarkably corrosion resistant.

The bent end of the folded conductor may be followed distally by anothercomponent such as a filament that takes the place of the foldedconductor in the multi-filar helical winding of other conductorsextending distally along the lead body. The filament is preferablynon-conductive and is attached to the bent end of the folded conductor,serving as a means of securing the bent wire end to the lead andpreventing it from rising significantly above the adjacent surface ofthe lead. The filament can be secured with a loop or a knot, preferablywith a knot that constrains the bent end of the conductor to preventcyclic deformation of the bend during flexing of the lead and thepotential for subsequent mechanical failure. One such knot is a loopedknot known as a cableman's hitch (also known as a cow hitch); this canalso be tied as a multiple cableman's hitch. This filament preferablyextends to the distal end of the multi-filar winding. The use of afilament having an outside diameter similar to the outside diameter ofthe insulated conductor allows for the possibility of maintainingisodiametricity and substantially the same filar spacing. Alternatively,a smaller diameter filament allows for decreased filar spacing (i.e., afiner pitch), thereby potentially aiding in flexibility and improvingelectrode surface area for the distal electrodes and minimizing the sizeof the attachment knot at the bend. More preferably, the non-conductivefilament is also folded in half, also resulting in a bent end thatpasses through the bent end of the folded conductor with first andsecond length segments of the folded filament extending distally in themulti-filar winding. A preferred material for the filament is afluoropolymer.

Alternatively, the bent end of the folded conductor may be secured tothe lead body using other means such as adhesives or short ties. Anexample of an adhesive is FEP which may be applied by first filling thebent end area with an FEP powder and subsequently wrapping over the areawith an FEP tape then heating the area above the melt point of the FEP.This may also increase insulative characteristics and serve as a sealagainst infiltration of fluids in that region of the lead. Similarly,films or tapes may be used to secure the bent end of a folded conductorto the lead body. In this embodiment, distally wound helical fibers canbe applied on top of the securing film or tape, without significantlyincreasing the lead body profile.

In an alternative embodiment, the uninsulated electrode conductorportions may be provided with a tubular covering of a porous polymericmaterial, wettable by body fluids to allow for charge conduction. Thistubular covering may optionally be connected to the end of the tubularinsulation that covers the insulated portion of the conductor.

The electrode portions of the lead are preferably provided with acovering of a conductive porous polymeric material such as porousexpanded PTFE, optionally containing a conductive material such ascarbon within at least a portion of the void spaces of the porousexpanded PTFE. The use of such a material provides a large electricallyconductive microscopic surface area to the adjacent tissue. Pore size istypically selected to limit or entirely preclude tissue attachment.Optionally, an additional covering of porous ePTFE of a smaller poresize may cover another layer or layers of a porous ePTFE having a largerpore size if it is desired to limit tissue attachment while providing amore porous underlying covering. These porous materials may bebeneficially treated with a wetting agent such as polyvinyl alcohol(PVA) to enable the underlying electrode to promptly support and enhanceconduction by wetting out with body fluids upon implantation.

In another embodiment, the porous ePTFE, filled with conductive materialsuch as carbon, may be densified creating a substantially non-porous andconductive surface over the electrode portions precluding the need forthe film to rapidly wet out.

In another embodiment: various conductive polymers can be used in theelectrode regions.

For improved robustness of the conductive ePTFE film over the electrodeportions of the lead body, a finer pitch film angle and an oppositehelical lay from the conductors is desired. Film angle may be reduced toincrease tensile strength or to increase radial strength. The film anglemay also be adapted to affect elongation. In addition other methods forimproving robustness include using thinner, stronger conductive film,applying more layers of the conductive film, applying or adhering areinforcing member along the conductive film region, for example alongitudinal strip or helical wrap of a metal wire or polymer filament,fiber or tape, for example a substantially impermeable ePTFE/FEPinsulating tape. Alternatively a preformed, strength-adding web orbraiding of a polymer or metal, in tubular form, may be applied over theconductive film electrode and subsequently attached or reduced in innerdiameter to be affixed to the electrode region. A strengthening member,including one which is impermeable, may also be added over or adhered tosubstantially all of the conductive film covered electrode andsubsequently perforated to allow conduction through said perforations.Such perforations may be formed using a laser suitable for perforatingonly the outer strengthening layer and not the conductive film below. Anexample of a puncturable strengthening member is the substantiallyimpermeable ePTFE/FEP insulating tape. A radiopaque or echogenic markermay also be incorporated into or with a strengthening member.

Each of the electrodes along the length of the lead proximal of the tipelectrode (i.e., the pacing electrode) is provided with acircumferential (annular) gasket ring or seal component at each end ofthe electrode. Alternatively, the seal material may be provided overmuch or even all of the entire length of the non-electrode portions ofthe lead, and may also be provided under the conductors along nearly theentire length of the lead. The preferred seal material is an elastomericmaterial and is intended to prevent body fluids from penetrating intothe insulated portions (i.e., non-electrode portions) of the lead whilethe adjacent electrode portions are, via the covering of the porousand/or electrically conductive film, in direct electrical contact withbody fluids. Preferred elastomeric materials include thermoplastics andfluoroelastomers. Particularly preferred is a thermoplasticfluoroelastomer copolymer oftetrafluoroethylene/perfluoromethylvinylether (TFE/PMVE) as taught inU.S. Pat. No. 7,049,380 and published US Patent applicationUS20060198866, both to Chang et al. These materials can also be used fortheir adhesive properties.

Preferred conductor insulating materials are fluoropolymer films thatoffer excellent insulation properties, good biocompatibility and minimaltissue attachment. As noted above, a substantially impermeable ePTFE/FEPinsulating tape is particularly preferred. In the interest of the leadhaving a minimal diameter, these materials may be effectively used invery thin forms. Thicker versions or additional layers of these samematerials may be used if it is desired to create a lead with increasedinsulation properties and/or mechanical properties such as increasedtensile strength, crush resistance, and/or improved abrasion resistance.A porous ePTFE tape, made as taught by U.S. Pat. No. 5,476,589 toBacino, and provided with a coating of FEP as taught by U.S. Pat. No.6,159,565 to Campbell et al., may also be added to portions of theoutside of the substantially impermeable ePTFE/FEP insulation ifadhesion of other materials to insulated conductors or outer lead bodyis desired (e.g., materials such as silicone or a fluoroelastomercopolymer).

The materials comprising the lead may optionally be heat set to form acurve or bend at the distal end during manufacturing. The helicalconductor construction provides torqueability that allows steerabilityof a curved distal end of the lead reducing the need to exchange curvedand straight stylets during implant. Additionally, the curved distal endcan reduce pressure on tissue, lowering the risk of tissue perforation.The curved distal end can also improve the ability to fixate the leadtip, for example more septally in the right ventricle, which may beclinically preferred.

All or part of the outer surface of the insulated portions of the leadmay be beneficially provided with a coating of the previously describedthermoplastic fluoroelastomer copolymer TFE/PMVE loaded with an elutabletherapeutic agent as taught in published US Patent applicationUS20060198866 to Chang et al. Therapeutic agents contemplated include,but are not limited to, antithrombotic agents, anticoagulants,antiplatelet agents, thrombolytics, antiproliferatives,anti-inflammatory, hyperplasia and restenosis inhibitors, smooth musclecell inhibitors, antibiotics, antimicrobials, analgesics, anesthetics,growth factors, growth factor inhibitors, cell adhesion inhibitors, celladhesion promoters and drugs that may enhance neointimal formation suchas the growth of endothelial cells. In one embodiment, said agent is ananti-inflammatory agent. In another embodiment, said anti-inflammatoryis a steroid such as dexamethasone sodium phosphate. In anotherembodiment, the therapeutic agent may include heparin.

U.S. Pat. No. 5,874,165 to Drumheller describes attaching varioustherapeutic agents to PTFE substrates.

These coatings may also be applied directly to the fixation helix.Additionally, the fluoroelastomer copolymer TFE/PMVE or other polymericcoatings, with or without therapeutic agents, may be used on the helixto vary the conductive surface to control current density and impedance.This may include insulative coatings that partially cover the helix,thin coatings that cover all or most of the helix but still allow adesired conductivity, or coatings filled with conductive material suchas carbon or metal particles. Additionally, a fluoropolymer coatingcontaining carbon for conductivity has a lower thermal conductivity thana bare metal helix, sensing ring or defibrillation electrode. Lowerthermal conductivity can increase MRI compatibility by reducing tissuedamage due to heating of the helix or other electrodes during exposureto fields associated with magnetic resonance imaging.

In an effort to provide optimal mechanical and electrical properties ina lead, MP35N DFT wire is typically used as the conductor of choice forthe defibrillation and pacing/sensing circuits. Wire made from thisalloy (mainly Ni, Co, Cr and Mo) is biocompatible and has excellentstrength and fatigue resistance for long-term use and survivability inan implantable lead. This wire also contains a silver core componentknown as “drawn filled tube” or DFT.

This silver core typically ranges from 25-41% in filar cross-sectionalarea and provides a low electrical impedance or resistance to delivercurrent with minimal energy loss; 28% silver has produced good results.Fort Wayne Metals (Fort Wayne Ind.) sells a fatigue-resistant version ofthis wire (either as solid wire or multi-stranded wire) designated as35NLT. Given the transition metals found within 35NLT, the surface ofthis wire may be prone to oxidation when used as an anode (receivingcurrent) in a circuit. This oxidation may lead to significant pittingand/or corrosion of the wire depending on the amount of current usedover a period of time. To address this issue, one or more noble metalsmay be useful as an outer layering on the wire (applied, for example byphysical vapor deposition (PVD)) or alternatively as the entire wire.Noble metals such as tantalum, platinum, palladium and titanium andtheir alloys are less susceptible to oxidation or corrosion when used aseither the outer surface of a wire delivering current or as the entirewire. In another embodiment, a noble metal wire, preferablyplatinum-iridium, may be coiled over a wire or multi-stranded wire toprovide corrosion-resistance to the base wire. The diameter of the noblewire is preferably sized to be similar to the insulation thickness onthe conductor wire to provide a relatively consistent diameter from theconductor portion to the electrode portion. This embodiment may becombined with insulation material between or beneath the noble wire tofurther improve corrosion-resistance.

In cardiac applications, the electrical connector located at theproximal end of the lead is preferably an “IS-4” or “DF-4” type that isa single male connector having multiple contacts for connecting the leadconductors to a power or sensing and control source that is usuallyimplanted (sometimes referred to as a “generator”). One IS-4 or DF-4connector embodiment includes an inner tubular component featuring slotsor channels through which some of the lead conductor ends are passed.Contact rings made of a conductive material (e.g., stainless steel,MP35N, titanium, platinum alloy or other corrosion resistant materials)alternating with insulating rings, are co-axially fitted over thetubular member and conductor ends, with the conductor ends electricallyconnected to the inner surface of the contact rings by means such as aninterference fit and/or resistive welding.

In another embodiment, the contact rings include axially-orientedapertures beneath their exterior surface that allow insulated leadconductors to pass through the contact rings and connect to a moreproximal contact ring These rings may then be over-molded with aninsulative material, such as polyurethane or silicone. Anotherembodiment of the connector includes contact rings having preferablyintegral legs bent inwardly toward an insulating inner tube centeredwithin the connector. The inner tube is preferably threaded on at leastthe end portion of more preferably entirely. Both the inner tube and thecontact legs pass through adjacent contacts to the distal end ofconnector. Each contact leg is spaced axially and radially from theother contact legs. The spaced-apart contact legs are then over-moldedwith preferably a biocompatible polyurethane or silicone. The conductorsare connected to the distal end of each appropriate contact leg vialaser-weld, crimping, or similar attachment means which may also includea sleeve component. The distal end of the legs may be made larger inarea or thickness than the proximal portion of the legs to maketermination to the conductor easier. One advantage to this design isthat all conductors can be terminated in the connector at one region ofthe connector (preferably the distal region) rather than having to beterminated at each contact ring. These connections are then over-moldedwithin a strain relief. The strain relief may optionally include acomponent to guide the conductors to the connection point and ensureproper spacing and orientation for proper isolation and mechanicalrobustness. An end cap is threaded onto the proximal end of the innertube and seats inside the most proximal contact capturing the pinconnected to the pacing coil allowing it to rotate for fixation of theactive tip located at the opposite end of the lead.

Alternatively, other connectors can be used including “IS-1” or “DF-1”connectors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a typical implantable lead assembly asdescribed herein; the embodiment depicted includes defibrillator andsensing/pacing electrodes.

FIG. 2 is a perspective view of a portion of the length of a lead suchas shown in FIG. 1, excluding outer coverings.

FIG. 2A is a perspective view of a portion of the length of a leadsimilar to FIG. 2 but showing insulation over the bent end region of theconductive wire.

FIG. 3 is a side perspective view of a typical described lead showingeach of the uninsulated bare wire electrodes having bent ends secured bynon-conductive filaments, excluding outer coverings.

FIG. 3A is a side view of a lead showing the use of a knot with anon-conductive filament to secure the bent end of an uninsulated barewire electrode.

FIG. 3B is a top view showing the use of a cableman's hitch formed witha non-conductive filament to secure the bent end of an uninsulated barewire electrode.

FIG. 3C shows a top view of the knot, filament and bent electrode end ofFIG. 3B with the addition of a polymer tube insulating sleeve.

FIG. 3D shows a top view of a filament with a multiple cableman's hitchto attach the non-conductive filament to the bent end of an uninsulatedbare wire electrode.

FIG. 3E is a side view of a portion of the length of a lead showing theuse of adhered non-conductive tabs to secure the bent end of anuninsulated bare wire electrode.

FIG. 3F is a perspective view of an uninsulated bare wire electrodelocated along a length of wire between two insulated portions of thesame wire.

FIG. 3G is perspective view of the uninsulated bare wire electrode shownin FIG. 3F that has been provided with a covering of a porous polymericmaterial that allows for electrical charge conduction through thethickness of the covering.

FIG. 3H is a side view of an uninsulated bare wire electrode with thininsulation and an uninsulated platinum iridium wire coil.

FIG. 3I is a transverse cross-section of the uninsulated bare wireelectrode with thin insulation and an arc length of a platinum iridiumwire coil shown in FIG. 3H.

FIG. 3J is a side view of lead body with the electrode described inFIGS. 3H and 3I.

FIG. 3K is a perspective view of a standard (single) cableman's hitchtied to the end of the bent portion of the electrode described by FIGS.3H and 3I.

FIG. 3L is a longitudinal cross-section showing an alternativeembodiment with a platinum iridium wire coil in contact with theconductor adjacent to each end of the electrode portion of conductor.

FIG. 4 is a longitudinal cross section of an uninsulated bare wireelectrode (e.g., the distal defibrillator electrode) that does notinclude an outer platinum iridium coil showing the preferred outercoverings.

FIG. 4A is a longitudinal cross section of an uninsulated bare wireelectrode (e.g., the SVC electrode) that includes an outer noble metalcoil showing the preferred outer coverings including tapered filmtransitions.

FIG. 4B is a longitudinal cross section showing pitch change of themulti-filar windings when an electrode terminates at a bent end and isreplaced in the winding sequence by an uninsulated filament of diametersmaller than the electrode.

FIG. 5 is a longitudinal cross section describing the attachment of thepacing electrode (including fixation member) to the distal end of thelead.

FIG. 6 is a perspective view of a distal lead tip assembly provided witha covering of a therapeutic agent eluting polymer and containing anactive attachment component (e.g., helical fixation member).

FIG. 7 is a longitudinal cross section showing the construction of onedistal lead tip assembly embodiment.

FIG. 8 is a longitudinal cross section showing the construction of analternative distal lead tip assembly embodiment.

FIGS. 9A and 9B are longitudinal cross sections of a tip housingprovided with a flexible polymeric tip flanges outwardly when the tip isaffixed to the surface of the heart as shown in FIG. 9B.

FIGS. 10A and 10B are longitudinal cross sections of a tip housing thatincorporates a flexible shape-memory polymer member that extends beyondand flanges outward from the distal end of the tip when the tip isaffixed to the surface of the heart as shown in FIG. 10B.

FIGS. 11A and 11B are longitudinal cross sections of a tip housingprovided with an extension of the tip housing formed from a flexiblepolymer member that compresses and flanges outwardly from the distal endof the tip when the tip is affixed to the surface of the heart as shownin FIG. 11B.

FIGS. 12A and 12B are longitudinal cross sections of a tip housingprovided with a flexible shape-memory polymeric ring that flangesoutwardly from the distal end of the tip when pushed distally by theextending fixation member during affixing of the tip to the surface ofthe heart as shown in FIG. 12B.

FIGS. 13A and 13B are longitudinal cross sections of a tip housingprovided with an outer coating of a biocompatible polymeric hydrogel atthe distal end of the housing that expands by absorption of body fluidsfollowing implantation as shown in FIG. 13B. FIG. 13B also describes theappearance of a bioabsorbable flange as it would appear prior to andimmediately after implantation and prior to subsequent bioabsorption.

FIGS. 14A and 14B are respectively a perspective view and an end view ofa tubular tip housing provided with a pair of longitudinally orientedslots with the material of the tip housing between the adjacent slotsfolded inwardly to serve as a thread guide for a helical fixationmember.

FIGS. 15A and 15B are respectively a perspective view and an end view ofa tubular tip housing provided with a pair of helically oriented slotswith the material of the tip housing between the adjacent slots foldedinwardly to serve as a thread guide for a helical fixation member.

FIGS. 16A and 16B are respectively a perspective view and an end view ofa tubular tip housing provided with a pair of longitudinally orientedslots with the material of the tip housing between the adjacent slotsextending beyond the length of the tip housing and folded inwardly toserve as a thread guide for a helical fixation member.

FIG. 17 is a side view of a preferred electrical connector.

FIGS. 18A and 18B are respectively longitudinal and transverse crosssections of an electrical connector with a slotted tube.

FIGS. 19A-19E describes an alternative embodiment of the electricalconnector having contact rings provided with legs that extend distallyto connect with conductors from the lead body.

FIGS. 20A and 20B shows an alternative embodiment of an electricalconnector wherein insulated lead body wires can pass through aperturesprovided in the contact rings to allow them to extend and connect to amore proximal contact ring.

FIGS. 21A and 21B are respectively a longitudinal cross section and aside view that describe an electrical connector with a channeled tubeintended to allow passage of lead body wires and to allow a selectedwire to connect with the appropriate contact ring; FIGS. 21C-21E aretransverse cross sections taken at different contact rings of thisconnector.

FIGS. 22A and 22B show an inner portion of the strain relief intended toimprove the lead body conductor transitions to an electrical connector.

FIG. 23 is a schematic side view of an abrasion tester for evaluatingthe abrasion resistance of an implantable lead.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a typical implantable lead assembly 10as described herein, showing a proximally-located electrical connector12 to enable lead 10 to be connected to a suitable power source orsensing and control system 11, the proximal defibrillator electrode 14,the distal defibrillator electrode 16, the sensing electrode 18 and thedistal tip electrode assembly 20 attached at the distal end of lead 10by tip connection region 19. Lead 10 also includes intervening insulatedlength portions 13 and 15, as well as seal components 17 located at eachend of both defibrillator electrodes 14 and 16. It is apparent that anyor all of the length portions shown can be made to any desired length.

FIG. 2 is a perspective view of a portion of the length of a lead 10such as shown in FIG. 1, excluding outer coverings. The portion shown inFIG. 2 is indicated by the break lines “2” shown in FIG. 1 and includesthe proximal defibrillator electrode 14. Portion 13 includes threeconductor “first and second length segments” 22, 24 and 26 shown in ahelically wound, multi-filar arrangement that has been formed over themulti-filar winding liner 23. Helically wound pacing electrode conductor21 is located within the lumen formed by liner 23 and extends tofixation member 112 located at the distal tip of the lead 10. Pacingelectrode conductor coil 21 is provided with an outer insulativecovering that is not shown here.

FIG. 2A is a perspective view of a portion of the length of a leadsimilar to FIG. 2 but showing insulation 27 over the bent end 22 b ofthe conductive wire 22 e. It is apparent that insulation may beoptionally used over any or all of bent ends 22 b, 24 b and 26 b. Pacingelectrode conductor coil 21 is provided with an outer insulativecovering that is not shown here. The covering over pacing electrode coil21 is preferably formed by helically-wrapping the coil at least oncewith the substantially impermeable ePTFE/FEP insulating tape describedpreviously, with the FEP coated side facing against the surface of coil21. Alternatively, the covering can be formed by extrusion or placingthe coil in an insulative tubular member. A small amount of clearance(e.g., about 0.05 mm) is provided between the outer covering of pacingcoil 21 and the inner lumen of liner 23 in order that coil 21 may berotated to drive the fixation member 112 into or withdraw it from thecontacted tissue.

The conductor first and second length segments 22, 24 and 26 arepreferably multi-stranded wires that add to the flexibility and flexlife of the lead. They are provided with a thin, strong, high dielectricstrength insulation covering that is biocompatible. A preferredinsulation for use around these stranded wire conductors is provided bytape-wrapping with the previously described substantially impermeableePTFE/FEP insulating tape.

Each of the three conductive first and second length segments 22, 24 and26 constitutes a distinct voltage conductor for three differentelectrodes, respectively the proximal defibrillation electrode 14 (shownin FIG. 2), the sensing electrode 18 and the distal defibrillationelectrode 16 (electrodes 16 and 18 not shown in FIG. 2). It is apparentthat the sequence of the arrangement of conductors and electrodes can beas desired, just as it is apparent that any desired number of conductorsand electrodes can be chosen. Each of these conductor first and secondlength segments 22, 24 and 26 are formed from a length of a singleconductor that has been folded approximately in half as will be furtherdescribed.

Where insulated segment 13 transitions to electrode 14, it is seen thatthe insulation is removed from conductor first and second lengthsegments 22 at the proximal end of electrode 14. The electrode 14 thencomprises an uninsulated portion of first and second length segments 22,shown as 22 e. The bare, uninsulated portion 22 e of electrode 14terminates at its distal end in a 180° bend 22 b in uninsulated wire 22e, where it is seen how first and second length segments 22 are simplytwo halves of the same conductor 22 that has been folded in half tocreate 180° bend 22 b.

At bend 22 b, a non-conductive filament 32 has been passed throughconductor bend 22 b thereby creating filament bend 32 b. It is apparentthat filament 32 has been folded in half (i.e., bend 32 b) in a mannersimilar to the way conductor 22 has been folded in half, with the halvesof filament 32 creating filament first and second length segments 32that continue to the distal end of lead 10 in the multi-filar windingwithin the winding space previously occupied by conductor first andsecond length segments 22 prior to its ending at conductor bend 22 b. Itis likewise apparent how conductor bend 22 b is interlocked withfilament bend 32 b. Filament bend 32 b and filament first and secondlength segments 32 thus serve to secure wire bend 22 b to the surface oflead 10 (e.g., to the outer surface of winding liner 23). Distal toconductor bend 22 b and filament bend 32 b, non-conductive filamentfirst and second length segments 32 also serve to replace the filarspace previously occupied by conductor first and second length segments22 proximal to conductor bend 22 b. Non-conductive filament 32 ispreferably of a fluoropolymer material, desirable for the lubricity ofsuch materials and for resistance to process heating during constructionof the lead. ePTFE filaments are preferred for their strength andlubricity; such filaments may be made generally as taught by U.S. Pat.No. 5,281,475 to Hollenbaugh Jr. et al. Filaments may also comprisepolyetheretherketone (PEEK), fluorinated ethylene propylene (FEP),polyurethanes, etc. The use of non-conductive fluoropolymer filamentssuch as ePTFE is believed to contribute to the flexibility and flex lifeof lead 10. Filament 32 may be of a smaller diameter than conductors 22,24 or 26 if it is desired to create an even finer pitch in themulti-filar winding for enhanced flexibility.

Alternatively, filament 32 might constitute a film or tape over whichdistally extending conductors might be helically wrapped.

While it is stated that the filaments should be of nonconductivematerials, it would be possible (although less desirable) to usedimensionally compatible metal or metal-containing filaments to providethe space-occupying function of the filaments if they were insulatedfrom the other conductive components and preferably provided with anouter covering of an insulating material to isolate them electricallyfrom surrounding tissue.

The other two conductor first and second length segments 24 and 26continue distally beyond the lead portion 15 shown in FIG. 2, remainingin the multi-filar winding along with filament first and second lengthsegments 32 distal to conductor bend 22 b.

FIG. 3 is a side perspective view of a typical described lead 10 showingeach of electrodes 22 e, 24 e and 26 e but excluding outer coverings;this figure is broken into upper and lower views, with the upper portionportraying proximal defibrillation electrode 14 and the lower viewportraying distal defibrillation electrode 16 and the sensing electrode18. The upper view shows electrode 14 in a similar fashion as theperspective of FIG. 2. It is seen how for each electrode 14, 16 and 18(as one considers the lead from the proximal end to the distal end), therespective conductor first and second length segments 22, 26 and 24 arereplaced by non-conductive filament first and second length segments 32,36 and 34 following the ends of electrode conductor first and secondlength segments 22 e, 26 e and 24 e at the respective interlocked 180°bends of the electrode conductors and non-conductive filaments. It islikewise seen how the 180° bends of the beginning of each filament areinterlocked by being looped through the 180° bends that end eachelectrode conductor. Alternatively, it is apparent that one end of afilament may be tied around bend 22 b, with the remainder of the lengthof the single filament (not folded and doubled) extending toward thedistal end of the lead.

FIG. 3A is a side view of a portion of the lead 10 showing analternative use of a filament 33 to tie down the bent end of electrode22 e. Filament 33 is wrapped once around the circumference of lead 10(e.g., winding liner 23) and passes through the bent end of electrode 22e; the two ends of filament 33 are secured with knot 33 k. FIG. 3B is atop view showing the use of a knot 33 k, in this case a cableman'shitch, formed with a non-conductive filament (32, 34 or 36) to securethe bent end (22 b, 24 b or 26 b) of an uninsulated bare wire electrode22 e, 24 e or 26 e. FIG. 3C shows a top view of knot 33 k, filament 32,34 or 36, and bent electrode end 22 b, 24 b or 26 b of FIG. 3B with theaddition of a polymer tube insulating sleeve 38. FIG. 3D shows a topview of a filament (32, 34 or 36) with an alternative knot 33 k (e.g., amultiple cableman's hitch) attaching the non-conductive filament 32, 34or 36 to the bent electrode end (22 b, 24 b or 26 b).

FIG. 3E is a side view showing the bent end 22 b (or 24 b or 26 b) ofelectrode 22 e (or 24 e or 26 e) secured by securing tab 35. Such a tabmay be made from various materials including the previously describedsubstantially impermeable ePTFE/FEP insulating tape and secured by heatbonding the thermoplastic FEP coating to the underlying surface. Otheradhesion methods may also be used.

FIG. 3F is a perspective view of a middle portion of a conductor such asconductor 22 prior to being folded in half to create parallel first andsecond length segments 22. It will be appreciated that the length of theexposed conductors located on either side of the bend may be equal ormay be different. The uninsulated section 22 e that forms electrode 14is seen without the insulation that covers the remainder of the lengthof conductor 22. FIG. 3G is another perspective view that shows how theuninsulated section 22 e may be provided with a covering of a porousmaterial that allows penetration of body fluids and consequently iselectrically conductive through its thickness. As noted above, apreferred porous material is porous ePTFE film; more preferred is porousePTFE film that contains a conductive material such as carbon in aportion of the void space of the material. The figures show how theporous covering material may be used to increase the diameter of theuninsulated section 22 e of FIG. 3F to match that of the adjacentinsulated portions of conductor 22, thereby creating covered electrodeportion 22 ec shown in FIG. 3G and aiding in maintaining the preferredisodiametric character of lead 10. It is apparent that this method ofincreasing the diameter of an uninsulated conductor may be used whetherthe uninsulated portion is located between the conductor ends oralternatively located at one end of a conductor.

FIG. 3H is a side view of a portion of conductor 22, 24, 26 with anelectrode portion 22 e, 24 e, 26 e. For this embodiment, the thickerinsulation 29 covering conductor 22, 24, 26 is transitioned to a thinnerinsulation 31 such as the previously described substantially impermeableePTFE/FEP insulating tape. Noble metal wire 28 is tightly coiled ontothinner insulation 31 with appropriate tension and heat to createelectrical communication (conductivity) between noble metal wire 28 andbase conductor 22, 24, 26. FIG. 31 shows a transverse cross section ofnoble wire 28 tightly wound around thinly insulated 31 conductors 22 e,24 e or 26 e. The ends 37 of the noble wire 28 are secured in place andsealed (insulated) with an elastomeric adhesive 30, preferably afluoroelastomer adhesive such as the TFE/PMVE copolymer taught by Changet al. as described previously. Noble wire 28 shown in FIG. 3H is ofround transverse cross section, but may alternatively be a flat orshaped wire. Similarly, the thinner insulation 31 may cover the entirelength of conductor 22, 24, 26 with the noble metal wire 28 coiled downthe entire length of conductor 22, 24, 26 and the thicker insulation 29over both the thinner insulation 31 and the noble metal wire 28 in thenon-electrode portions. This may include a varying pitch, with theelectrode portion having a tight (finer) pitch and the portions underthe thicker insulation having an open (coarser) pitch.

In another embodiment, the thin insulative material 31 may be appliedbetween the noble metal wire coils (after winding the noble metal coil28 onto bare wire conductor 22 e, 24 e or 26 e) leaving the outersurface of the noble wire coil 28 exposed for conductivity. This mayinclude placing insulative material 31 over noble metal coil 28, forcinginsulative material 31 between coils 28 through means such as heatingand then exposing the tops of coil 28 for conductivity.

The electrodes of FIG. 3H have been shown to be highlycorrosion-resistant.

FIG. 3J is a side view of a portion of lead body 10 showing noble wire28 coiled over thinly insulated electrode portion 22 e of conductor 22.

FIG. 3K is a top view showing the use of a knot 33 k, in this case acableman's hitch, formed with a non-conductive filament (32, 34 or 36)to secure the bent end (22 b, 24 b or 26 b) of a thinly insulated wireelectrode 22 e, 24 e or 26 e provided with a tightly wound noble wirecoil 28.

Additionally, as shown by the longitudinal cross section of FIG. 3L, thenoble metal wire 28 may be coiled onto bare conductor 22 e, 24 e or 26 ein a stripped section, then continue over a fully (e.g., thickly)insulated section 29 of conductor 22, 24 or 26 and then coil over asecond stripped section 22 e, 24 e or 26 e. These stripped sections maythen be additionally covered with an insulation 30 to prevent fluidpenetration. The center section, provided with a covering of aconductive polymer (e.g., carbon-loaded ePTFE film), functions as anelectrode.

FIG. 4 is a longitudinal cross section of electrode (the distaldefibrillator electrode) that describes preferred outer electrodecoverings. The section shown describes distal defibrillation electrode16 but is typical for electrodes 14, 16 and 18 with regard to outercoverings. While a specific combination of coverings is shown, it isapparent that these coverings may be applied in a variety ofthicknesses, number of layers, materials, etc.

It is noted that FIGS. 4, 4A and 4B do not include pacing conductor coil21 or inner liner 23 to allow for clarity of the description of thecomponents shown.

Seal components 17 are provided at opposing ends of electrode 16 and areintended to prevent body fluids from making their way into thenon-electrode, insulated conductor portions of the length of lead 10.Seals 17 are comprised of an elastomeric material with fluoroelastomerspreferred. Particularly preferred is the previously described TFE/PMVEfluoroelastomer copolymer. These seals may also be made bycircumferentially wrapping the area where it is desired to provide theseal component with a composite tape made from a film of ePTFE providedwith a coating of an elastomer such as the TFE/PMVE copolymer. Thecircumferentially wrapped ePTFE provides strength and addscircumferential compression when heated, while the thermoplasticTFE/PMVE is allowed to flow into the underlying shape of the insulatedconductors during the controlled manufacturing heating step. Thesecomposite ePTFE and fluoroelastomer tape materials are also described byChang, et al. in U.S. Pat. No. 7,049,380 and published US Patentapplication US 20060198866.

The outer surface of electrode 16 is provided with a covering 48 of aporous, electrically conductive film such as carbon-loaded ePTFE film.The number of wraps (two layers are shown) will be a function of thetotal porosity of the covering, the conductivity of the covering and thedesired thickness of the covering.

The insulated portion of the lead on either side of electrode 16 and theseal components 17 is provided with a wrapping 46 of an ePTFE film.While this film may be (for convenience) the same carbon-loaded ePTFEfilm covering 48 used over the electrode, alternatively, anon-conductive film may be used. In another alternative, the compositeePTFE and fluoroelastomer tape described above may also be used. Twolayers of wrapping 46 are shown, but again this thickness will bedetermined by desired design criteria.

Following the application of the above-described coverings of lengthportions 13 15, and 17 of lead 10, the entire length of the lead(including the insulated portions and the electrode portions) may beprovided with a wrapped covering 44 of a porous ePTFE film. One layer 44is shown, but again this thickness will be determined by desired designcriteria.

Finally, the insulated portions of the length of the lead 10 areprovided with a covering 42 of the substantially impermeable ePTFE/FEPinsulating tape used previously for insulating individual electricalconductors. This covering may also be applied as a helicaltape-wrapping. While two layers 42 are shown, the thickness will bedetermined by desired design criteria.

FIG. 4A is a longitudinal cross section showing the tapered transitions47 between the conductive film 48 (e.g., carbon-loaded ePTFE film)covering the electrode portions, and the covering 42 over the adjacentinsulated portion 13, 15 or 17, preferably the previously describedsubstantially impermeable ePTFE/FEP insulating tape. These taperedtransitions 47 may extend over longer lengths than described by FIG. 4A.In one embodiment, the insulative outer body film 42 is helicallyoverwrapped with substantially impermeable ePTFE/FEP insulating tape(not shown) slightly overlapping onto the conductive outer body film 48.

FIG. 4B is a longitudinal cross section showing pitch change (differencebetween angles 55 and 56) resulting from the use of filament 32 toreplace conductor 22 as it terminates at bent end 22 b (not shown), thefilament 32 of this embodiment being of smaller diameter than insulatedconductor 22. The resulting finer pitch 56 enhances flexibility in thatportion of the lead. Enhanced flexibility is believed to be desirable atthe distal end of the lead 10 to prevent tissue perforation at the pointof tissue attachment.

FIG. 5 represents a side cross sectional view of the junction betweenthe distal tip assembly 20 (further described below) and lead 10 showingone construction suitable for attaching the distal tip assembly 20 tothe distal end of lead 10. Said junction comprises a bushing 99 (seealso FIG. 6) which abuts against tubular tip housing 105 and the distalend of the body of lead 10. Bushing 99 includes a sleeve portion 98 thatfits within tubular tip housing 105, and flange portion 97 for attachingbushing 99 to the tip housing 105. Bushing 99 is preferably made from anon-conductive material such as plastic. Preferred plastic materials arefluoropolymers such as PTFE or FEP. Sleeve portion 98 of non-conductivebushing 99 is fitted into the proximal end of tubular tip housing 105(see below description), with flange 97 abutting the proximal end oftubular tip housing 105 and the distal end of the body of lead 10. Allthree components are attached by wrapping one or more layers of a thinimpermeable film 42 (such as the substantially impermeable ePTFE/FEPinsulating tape used previously for insulating individual electricalconductors) around the outer surface of tubular tip housing 105, flangeportion 97 of bushing 99 and the distal end of the body of lead 10.Bushing 99 further comprises an internal chamfer 50 which willaccommodate the distal end of insulating film layer 44 andnon-conductive filaments 32, 34, 36 that are flattened (32 c, 34 c, 36c) due to the pressure exerted by the several layers ofcircumferentially wrapped insulating tape 52 in region 52 cw.

Filaments 32, 34 and 36 are shown disposed over a multi-filar windinginner liner 23 which extends for the entire length of lead 10 and alsounderlies helically wound conductors 22, 24 and 26. Multi-filar windingliner 23 is preferably a fluoropolymer layer that provides a lubriciousluminal surface beneath the helically wound conductors 22, 24 and 26 andthe helically wound filaments 32, 34 and 36, and that aids therotational capability of pacing coil 21 that resides in this luminalspace. Additionally, polymeric multi-filar winding liner 23 can serve asa release agent from any mandrel used temporarily as a supportingsurface for the winding of conductors 22, 24 and 26 as well as filaments32, 34 and 36. This layer 23 may be made by winding layers of ePTFE tape(e.g., substantially impermeable ePTFE/FEP insulating tape) over atemporary construction mandrel and heat bonding them together prior towinding the conductors and filaments.

Pacing coil 21 is also preferably provided with an outer covering 88 ofa polymeric material of the previously described substantiallyimpermeable ePTFE/FEP insulating tape. Typical clearance providedbetween the outer covering 88 of pacing coil 21 and the luminal surfaceof multi-filar winding liner 23 may be, for example, about 0.02-0.06 mm.

As shown in FIG. 5, the transition from the distal end of the body oflead 10 to distal tip assembly 20 comprises several layers of film. One(or more) of the layers is the continuation of layer 44 (see FIG. 4),which comprises a porous ePTFE film that is helically wrapped on lead10, as described above. Next, multiple layers 52 of an insulating filmsuch as the previously described substantially impermeable ePTFE/FEPinsulating tape are wrapped circumferentially around the distal end ofthe body of lead 10 adjacent to and immediately proximal to bushing 99.These wrapped layers 52 of tape are used to secure the distal ends offilaments 32 c, 34 c and 36 c, and to match the diameter of the distalend of lead 10 in region 52 cw to the outside diameter of tubular tiphousing 105 so that lead 10 and tip housing 105 are isodiametric (each“layer” 52 may comprise multiple wrappings of tape). Said substantiallyimpermeable insulating tape 52 is used to prevent tissue from growinginto lead 10 and serves as an insulator. Layer(s) 42, continued from thebody of lead 10, are helically wrapped around the distal end of the bodyof lead 10, flange 97 of bushing 99 and the outer surface of tubular tiphousing 105. Other materials may be provided over the layers 42 ifdesired for other purposes such as therapeutic agent elution, as will befurther described.

FIG. 6 is a perspective view of one embodiment of the distal tipassembly 20 of lead 10 (hereinafter referred to as the “tip”). As seenin FIGS. 6 and 7, s tip 20 is constructed from a tubular tip housing 105comprising a sidewall 104 and a substantially open end 102, a fixationmember 112, and at least one layer of substantially impermeableePTFE/FEP insulating tape covering a portion of said tip housing and atleast a portion of said open end. Also shown is flange 97 ofnon-conductive bushing 99, as described above. Tip assembly 20 in FIG. 6depicts a sprayed on layer of the previously described thermoplasticfluoroelastomer TFE/PMVE 124, and includes eccentric hole 101 thatguides a helical fixation member 112 out of tubular tip housing 105. TheTFE/PMVE coating layer may optionally contain an elutable therapeuticagent including, but are not limited to, antithrombotic agents,anticoagulants, antiplatelet agents, thrombolytics, antiproliferatives,anti-inflammatory, hyperplasia and restenosis inhibitors, smooth musclecell inhibitors, antibiotics, antimicrobials, analgesics,anti-coagulant, anesthetics, growth factors, growth factor inhibitors,cell adhesion inhibitors, cell adhesion promoters and drugs that mayenhance neointimal formation such as the growth of endothelial cells. Apreferred therapeutic agent is an anti-inflammatory steroid such asdexamethasone sodium phosphate.

Tip assembly 20 is coupled to the medical lead (as described above) vianon-conductive bushing 99 which abuts against said tip assembly 20 andthe distal end of the body of lead 10. With bushing 99 fitted into tiphousing 105 as shown and abutted against the distal end of the body oflead 10, these components are attached to the distal end of lead 10 bywrapping multiple layers of substantially impermeable ePTFE/FEPinsulating tape around the outer surface of tip housing 105, bushing 99and lead 10 as previously described.

FIG. 7 illustrates a side cross sectional view of distal tip assembly20. The tip housing 105 is constructed from a tubular material having asubstantially open end 102 and sidewall 104. Tubular tip housing 105 canbe made from any durable, biocompatible material, for example PTFE,stainless steel, nitinol, or platinum. The tip housing 105 contains apost 106 which electrically couples coil 21 to a fixation member 112,which will be inserted into the tissue. Post 106 can be made from anybiocompatible, durable metal, most preferably stainless steel, althoughother conductive materials such as platinum, titanium or gold may alsobe employed. In one embodiment, a region of post 106 will be in closecontact with the inner wall of tip housing 105. This contact willprovide proper guidance to fixation member 112 as fixation member 112 isextended or retracted. In another embodiment, post 106 comprises asleeve portion 108. In another embodiment, coil 21 is placed into sleeveportion 108 of post 106 and held in place by spot or laser welding orcrimping. In another embodiment, a crimping mandrel 114 is inserted intocoil 21 and placed into sleeve 108 of said post 106 and crimped. Saidcrimping mandrel 114 supports said coil 21 during crimping so that saidcoil 21 is not collapsed during crimping. The coil 21 can be insulatedsuch as by wrapping with a film 88 (see FIG. 5; e.g., the previouslydescribed substantially impermeable ePTFE/FEP insulating tape) to keepcoil 21 tightly wound and can also serve as insulation to preventshorting and to improve torque transmission. If said coil 21 isinsulated, then the crimp 107 (see FIG. 5) will break outer covering offilm 88 to allow contact between the post 106 and the coil 21. Inanother embodiment, coil 21 is not insulated at the distal end so thatit can easily be electrically coupled to post 106. In another embodimentof the invention coil 21 is the pacing coil of lead 10 (as describedabove).

FIG. 7 also illustrates a fixation member 112 intended to provideattachment to tissues. The fixation member 112 can be made from anybiocompatible, durable and conductive material such as stainless steel,platinum, titanium, palladium, and their alloys. In one embodiment, saidfixation member 112 is a helical fixation member. In another embodiment,said helical fixation member 112 may be rotatably extended and retractedby rotation of the coil 21. Said helical fixation member 112 can besecured to post 106 by laser or spot welding, or by crimping, or byother methods known to those skilled in the art. Post 106 willelectrically couple the fixation member 112 to the coil 21 and alsoserve as an axial guide for fixation member 112. Guidance to helicalfixation member 112 may also be provided by means such as deformation103 formed in or attached to the distal end of the inner wall of thetubular tip housing 105; other guidance means such as a guiding pin mayalso be utilized.

FIG. 7 illustrates that distal tip assembly 20 may be covered by several“layers” of film. Each “layer” may comprise multiple wrappings of film.Thus the term “layer” is not limited to one wrapping, but may encompassany number of wrappings. In one embodiment, at least one layer is alayer substantially impermeable to fluids and tissue ingrowth. Saidsubstantially impermeable layer may also provide electrical insulation.As illustrated in FIG. 7, there may be several layers of film coveringthe side wall 104 and the opening 102 of tubular tip housing 105. Layer42 is a substantially impermeable layer that extends from side wall 104of the tip housing 105 to the body of lead 10, so that said tip assembly20 and body of lead 10 are coupled together, as described above. Thislayer 42 also serves to electrically insulate the tip housing. Layer 42may be applied by helically wrapping the substantially impermeableePTFE/FEP insulating tape, around the body of lead 10 and the tipassembly 20. In one embodiment, said layer 42 is the previouslydescribed substantially impermeable ePTFE/FEP insulating tape. Inanother embodiment, said distal tip assembly 20 may comprise anotherlayer of film 116. In this embodiment, layer 116 covers at least sidewall 104 and open end 102 of tip housing 105. In this embodiment, saidlayer 116 is “draped” over the open end 102 of tip housing 105, thuscovering opening 102 (with a drum-like covering) and said side wall 104.In another embodiment, said distal tip assembly 20 comprises anotherlayer of film 118 wrapped around side wall 104 and over layer 116. Inthis embodiment, film 118 may also be a substantially impermeable film.In another embodiment, said film is the previously describedsubstantially impermeable ePTFE/FEP insulating tape. Layer 118 can serveto keep layer 116 in place and also adds another layer of electricalinsulation to tip housing 105. In another embodiment, said tip assembly20 may comprise an additional layer of film 120 which is preferably apermeable layer. Said layer can be a porous ePTFE film provided with adiscontinuous (porous) coating of FEP. In this embodiment, layer 120 is“draped” over the tip assembly 20, thus covering said tip housingopening 102 (in a drum-like covering) and said side wall 104. Saidporous FEP-coated ePTFE film 120 can be attached to underlyingsubstantially impermeable tapes via the FEP coating acting as anadhesive. Said porous FEP-coated ePTFE film 120 may also provide aporous substrate for attachment of coatings such as a therapeutic agenteluting layer 124. In another embodiment, said distal tip assembly 20comprises another layer of film 122 wrapped around said side wall 104and covering layer 120. In this embodiment, said film 122 is preferablya porous film or tape such as ePTFE provided with a discontinuouscoating of FEP. This layer 122 can serve to keep layer 120 in place. Inanother embodiment, said distal tip assembly 20 may comprise atherapeutic agent eluting layer 124. In this embodiment said therapeuticagent eluting layer may comprise the previously described thermoplasticfluoroelastomer copolymer TFE/PMVE and a therapeutic agent as previouslydescribed. In another embodiment, the therapeutic agent elutingcopolymer can be sprayed onto said distal tip assembly 20 to create atherapeutic agent eluting layer 124. In another embodiment, saidtherapeutic agent eluting copolymer is incorporated into or coated on afilm that is applied over said distal tip assembly 20. In anotherembodiment, said therapeutic agent eluting copolymer can be provided asa pre-formed cover that can be placed over said tip assembly 20. Inanother embodiment, said tip can be dip-coated with the therapeuticagent eluting copolymer.

In other embodiment of the invention, said layers that cover opening 102have an eccentric opening 101 (FIG. 6) wherein said fixation member 112can pass though. Using films to cover opening 102 of said tip housing105 is beneficial because films are thinner, thus making the tipassembly 20 shorter in length. These films covering opening 102 alsoprovide additional surface area for therapeutic agent elution and mayminimize the likelihood of tissue trauma. In addition, the filmsmentioned above have the necessary strength to support helical fixationmember 112 as it threads through eccentric hole 101. Joining of distaltip assembly 20 to the distal end of the body of lead 10 as describedabove improves reliability through increased tensile strength and lowertorque requirements for extending and retracting fixation member 112.

The tip assembly 20 may also include a radiopaque marker to enhanceimaging of the location of the tip assembly 20 and/or fixation member112. This marker may be placed at any location along tip housing or overentire tip housing to provide a reference between the housing andfixation helix to indicate under fluoroscopy when fixation member 112 isfully extended and or retracted. Radiopaque markers may also be added tofixation helix and or post 106 or the internal lumen of tip housing 105.

Another embodiment of the invention depicts an alternative tip assembly20A as illustrated in FIG. 8 and generally constructed in a similarmanner as described above. FIG. 8 further depicts a tip assembly 20Athat comprises a copolymer cap 202. Said copolymer cap 202 furthercomprises a helical lumen 204 which guides helical fixation member 112as it extends or retracts. In one embodiment, said cap 202 is comprisedof a therapeutic agent eluting copolymer. In another embodiment, saidcopolymer is the previously described thermoplastic fluoroelastomercopolymer TFE/PMVE. Examples of therapeutic agents are discussed above.Copolymer cap 202 generally has a cylindrical shape with substantiallythe same outside diameter as the inside diameter of tip housing 105. Onemethod of making helical lumen 204 is to cure copolymer cap 202 with ahelical piece that mimics said helical fixation member 112, but is atleast one gauge thicker than said helical fixation member 112. Aftercuring cap 202 comprising said mimic, the mimic is removed fromcopolymer cap 202, leaving helical lumen 204. In another embodiment,helical lumen 204 can be created by methods known by those skilled inthe art.

Once copolymer cap 202 with helical lumen 204 is made, said cap 202 willbe placed at the distal end of said tip housing 105. Helical fixationmember 112 will be inserted into helical lumen 204 and cap 202 may abutor protrude slightly beyond the distal end of tip housing 105. Cap 202will be affixed to side wall 104 by wrapping at least one layer of film42 around cap 202 and side wall 104 of the tip housing 105. In oneembodiment, layer 42 is a substantially impermeable layer that extendsfrom the distal end of tip assembly 20A to the distal end of lead 10.This layer serves to electrically insulate tip housing 105 and to attachcap 202 to the side wall 104 of tip housing 105. This layer may beapplied by helically wrapping said substantially impermeable film aroundthe cap 202 and the tip housing 105. In one embodiment, saidsubstantially impermeable layer is the previously describedsubstantially impermeable ePTFE/FEP tape. Said tip assembly 20A can beattached to the body of lead 10 as described above.

FIGS. 9A and 9B are longitudinal cross sections of a tip housing 105provided with a flexible polymeric sleeve 126 that flanges outward whenthe tip 20 is affixed to the surface of the heart as shown in FIG. 9B.Sleeve 126 may be made of any suitably flexible and biocompatiblepolymeric material. Elastomeric materials capable of eluting therapeuticagents are preferred. A dissolvable coating over the outside of sleeve126 may be used to prevent a flange from expanding during implantation.

FIGS. 10A and 10B are longitudinal cross sections of a tip housing 105that incorporates an internal sleeve 128 of a flexible memory polymerthat extends beyond and flanges outward from the distal end of the tip20 when the tip is affixed to the surface of the heart as shown in FIG.10B. Sleeve 128 may be made of any suitably flexible and biocompatiblepolymeric material. Elastomeric materials capable of eluting therapeuticagents are preferred.

FIGS. 11A and 11B are longitudinal cross sections of a tip housing 105provided with an extension 130 of the tip housing 105 formed from aflexible polymer that compresses and flanges outwardly from the distalend of the tip 20 when the tip is affixed to the surface of the heart asshown in FIG. 11B. Extension 130 may be made of any suitably flexibleand biocompatible polymeric material. Elastomeric materials capable ofeluting therapeutic agents are preferred.

FIGS. 12A and 12B are longitudinal cross sections of a tip housing 105provided with a flexible shape memory polymeric ring 132 that flangesoutwardly from the distal end of the tip when pushed distally by theextending fixation member 112 during affixing of the tip 20 to thesurface of the heart as shown in FIG. 12B. Ring 132 may be made of anysuitably flexible and biocompatible shape memory polymeric material.Materials capable of eluting therapeutic agents are preferred.

FIGS. 13A and 13B are longitudinal cross sections of a tip housing 105provided with an outer coating 134 of a biocompatible polymeric hydrogelat the distal end of housing 105 that expands by absorption of bodyfluids following implantation as shown in FIG. 13B.

FIG. 13B also describes the appearance of a flange 134 made of abioabsorbable material as it would appear prior to and immediately afterimplantation, and prior to subsequent bioabsorption. Suitablebioabsorbable materials are well known in the art.

FIGS. 14A and 14B are respectively a perspective view and an end view ofa tubular tip housing 105 provided at the distal end with a pair oflongitudinally oriented slots 136 with the material of the tip housingbetween the adjacent slots 136 folded inwardly to form a tab 137intended to serve as a thread guide for a helical fixation member 112(not shown). One of slots 136 is longer than the other to provide thebent tab 137 with an angle to correspond with the pitch of the fixationmember 112.

FIGS. 15A and 15B are respectively a perspective view and an end view ofa tubular tip housing 105 provided with a pair of helically orientedslots 138 with the material of the tip housing 105 between the adjacentslots 138 folded inwardly to serve as a thread guide 139 for a helicalfixation member 112 (not shown).

FIGS. 16A and 16B are respectively a perspective view and an end view ofa tubular tip housing provided with a pair of longitudinally orientedslots 136 with the material of the tip housing between the adjacentslots extending beyond the length of the tip housing and folded inwardlyto form a bent tab 137 intended to serve as a thread guide for thefixation member 112 (not shown). In this embodiment it is apparent thatthe length of tab 137 as shown in FIG. 16A prior to bending extendsbeyond the end of tubular tip housing 105. One of slots 136 is longerthan the other to provide the bent tab 137 with an angle to correspondwith the pitch of the helical fixation member 112.

Finally, lead 10 is provided with a suitable electrical connector 12 atits proximal end in order that it may be quickly and reliably connectedto a power or sensing and control system 11. The connector 12illustrated in FIG. 17 and subsequent figures, and described below, isgenerally known in the electrophysiology art as an “IS-4” or “DF-4”connector. The connector 12 is made to be plugged into a receptacle in apower or sensing and control system 11 that accepts IS-4 or DF-4connectors or in a suitable adapter. The connector 12 comprises ringconnector terminals 304, isolation rings 320 and a pin connector 302.

FIG. 18A illustrates a side cross sectional view of connector 12.Connector 12 comprises an insulating sleeve 312, an insulating sleevelumen 310 and slots 314 through the wall of insulation sleeve 312 whichwill let first and second lengths segments 22, 24 and 26 described abovepass from the lumen 310 of insulating sleeve 312 to the exterior of theinsulating sleeve 312. The insulating sleeve 312 can be constructed fromany suitable non-conductive biocompatible material, for example, PEEK orPTFE. Pin connector 302 is made from an electrically conductive materialand comprises a counterbore 306 where a coiled conductor (not shown) canbe inserted. In one embodiment, said coiled conductor is the pacing coil21 described above. Said coiled conductor electrically couples the pinconnector 302 to the fixation member 112 of the distal portion of saidmedical lead, as described above. The proximal end of the coiledconductor can be secured in place in counterbore 306 by resistive orlaser welding, crimping or other methods known in the art. Pin connectorbearing 322 accommodates the pin connector flange 308 which in turn isretained axially by retainer cap 324; this assembly allows rotation ofthe pin connector 302 along its longitudinal axis. Rotation of pinconnector 302 will allow fixation member 112 to be inserted into orextracted from tissue, as described above.

FIG. 18A also illustrates contact rings 304. Contact rings 304 can bemade from metals such as stainless steel, MP35N, or platinum-iridiumalloy. Contact rings 304 are electrically coupled to the proximal ends318 of said first and second lengths segments 22, 24 and 26 describedabove. Said conductor ends 318 are stripped of insulation and enter thedistal end of the insulating sleeve lumen 310 and are threaded throughtheir respective slots 314 so that wire ends 318 are now on the exteriorside of the insulating sleeve 312. Wire ends 318 are then electricallycoupled to their respective contact rings 304. Said wire ends 318 can beinterference fit, resistance or laser welded, and/or crimped to theluminal surface of contact rings 304. Contact rings 304 are axiallyseparated and electrically isolated from one another by isolation rings320. Isolation rings 320 can be made from non-conductive biocompatiblematerial such as PEEK or PTFE. In one embodiment, said insulating sleeve312 comprises a groove or “landing” that can accommodate conductor ends318. This will make conductor ends 318 flush with the insulating sleeve312. In another embodiment, said insulating sleeve slots 314 areradially separated by 120°. The schematic transverse cross section ofFIG. 18B illustrates that the slots are radially separated (but does notdescribe the necessary axial separation). In addition, slots 314 arelongitudinally or axially separated along the length of the insulatingsleeve 312 as shown in shown in FIG. 18A. Said connector 12 may alsoinclude a strain relief sheath 326 that encloses the distal portion ofthe insulating sleeve 312 and sleeve support cap 328 and a proximalportion of the body of lead 10 (not shown). This sheath 326 can be usedto prevent contamination from entering the insulating tube lumen 310 andmay also serve as a means for gripping the lead connector for insertionor pulling lead connector 12 in and out of a power or sensing andcontrol system 11. Sheath 326 can be made from any suitable electricallyinsulative biocompatible material and is typically of a polymeric, orpreferably, an elastomeric material.

FIG. 19A shows a longitudinal cross section of another embodiment of aconnector 12. Connector 12 contains three contact rings 304, eachcontact ring having a leg 315 (preferably integral with the ring) withan inward bend 316. Each leg extends distally to a tube 317. Wherenecessary legs pass through any distally-located contact rings 304. FIG.19A shows only one of the three legs 315, while all three legs 315appear in the phantom side view of FIG. 19B (as well as cross sectionalview 19E). The distal end of each leg 315 has a tube 317 crimped orwelded over that end of the leg 315 with the opposite end of each tube317 left open to accommodate conductors (22, 24 and 26; not shown here)that can be crimped or welded inside that opposite end of theappropriate tube 317. The inner tube 319 is formed during theover-molding between and distal to the contact rings 304 with aninsulative polyurethane or silicone injection to provide insulationrings 320 between and adjacent to the contact rings 304. Retainer cap324 can be threaded onto the proximal end of the threaded inner tube 319to capture pin connector 302.

FIG. 20A shows a longitudinal cross section of an alternative embodimentof a connector 12. Connector 12 has contacts rings 304 with a pair oflarger diameter apertures 305 that insulated wire 22, 24 or 26 (notshown) can pass through and smaller hole(s) 307 that an uninsulated wireend (22, 24 or 26; not shown) can be terminated to through welding,crimping or similar. Additionally contact rings 304 have a center hole309 allowing for placement of a pacing coil or inner tube 319.

FIGS. 21A and 21B are respectively a longitudinal cross section and aside perspective view and FIGS. 21C, 21D, and 21E are transverse crosssections that describe an electrical connector 12 with a channeled tube321 intended to allow passage of lead body wires (not shown) and toallow a selected wire to connect with the appropriate contact ring 304.Connector 12 has an inner tube 321 with channels 323 and is made of aninsulative polymer such as PEEK. Each channel 323 goes from the distalend of the connector 12 to the appropriate contact ring 304. Conductors(not shown) travel from lead body 10 along the appropriate channel 323and then are terminated to the appropriate contact ring 304. Anyremaining space is then backfilled with an insulative polymer 329 suchas silicone or polyurethane, including spaces between and adjacent tocontact rings 304.

FIGS. 22A and 22B show perspective views of an inner strain reliefportion 327 of connector 12 allowing the helically wound conductors 22,24 and 26 in the body of lead 10 to transition into a larger pitch forconnection to connector 12. Inner strain relief portion 327 may includethree wire channels 325 to guide conductors 22, 24 and 26 and graduallyincrease the diameter at connector 12 from that of lead 10.

The described lead may be made with a variety of techniques andmaterials of desired dimensions. The following manufacturingdescriptions and dimensions are therefore not intended to be limiting.

First, a long length of wire for use as conductors 22, 24 and 26, suchas a 1×19 0.165 mm 35 NLT DFT (Ft. Wayne Metals Corp, Ft. Wayne, Ind.)stranded wire, is tape-wrapped with the previously describedsubstantially impermeable ePTFE/FEP insulating tape. The tape is ofabout 2.5 mm width and is applied with a pitch of about 2.5 mm with theFEP-coated side of the film facing away from the wire surface. Thetape-wrapped wire is heated to 320° C. for 20-45 seconds, i.e., a timesufficient to ensure that the construct is heated above the melt pointof the FEP. The wrapped wire is then wrapped again in the opposingdirection with a 3.3 mm wide tape of the same type at a pitch of 2.9 mmwith the FEP facing the wire surface. The wire is heated again above theFEP melt point.

The resulting insulated conductor wire, having a diameter ofapproximately 0.27 mm, is cut into two 320 cm lengths and one 220 cmlength. The integrity of the insulation may be tested at this time bysoaking the wires briefly in 100% isopropyl alcohol and then immediatelytransferring the wire to 9 g/liter saline. A suitable voltage source(e.g., a Quadtech Guardian 12KVDC Hipot Tester (Maynard Mass. 01754)) isconnected to both ends of each wire and 5 kV is applied for 15 seconds.Following testing the wires should be rinsed in de-ionized waterfollowed by a rinse in 100% isopropyl alcohol.

Next, the center portion of the length of each wire is stripped ofinsulation by suitable means (e.g., thermal stripping). The strippedlengths should be about 4.3 cm for one of the 320 cm samples and about34 cm for the other, and about 34 cm for the 220 cm long wire. Each ofthese wires is then folded in half at the center of the non-insulatedportion, creating a 180° bend at the center of the length of each wire.Finally, a sufficient length of ePTFE filament appropriate to reach thedistal end of the constructed lead (further described below), of about0.125 mm diameter, is inserted into the apex of the bend of each wireand tied at the bend using a surgeon's square knot and the excessfilament trimmed.

Both ends of a length of silver-plated copper wire (intended to serve asa construction mandrel) are placed into the chucks of a winding machine.The wire mandrel will be used as a temporary substrate upon which willbe wound the multi-filar windings of the above-described conductors. Thediameter of the wire mandrel is chosen to be sufficient to provide thenecessary clearance to allow a pacing conductor coil to be rotated inthe lumen of the multi-filar winding so that the fixation memberelectrode, attached to the distal end of the pacing coil, may be screwedinto or removed from heart tissue. The wire mandrels for the followingmay be optimized to be the smallest practical diameter that allows forthe necessary pacing coil clearance in order that the outside diameterof the finished lead is minimal.

The silver-plated copper wire is then tape-wrapped with a thin ePTFEtape having a thickness of about 0.04 mm and of about 6.4 mm width, witha pitch of about 3.8 mm in a right-hand lay. Another layer of tape iswrapped over this first wrapping, using a 6.4 mm width tape of the sametype used for the wire insulating process described above, applied witha 3.6 mm pitch in a right-hand lay with the FEP-coated side of the filmfacing away from the surface of the silver-plated copper wire. Next, athird layer is over wrapped with the same tape used for the first layerof wrapping, this time applied at a 3.0 mm pitch in a right-hand lay.Finally, another layer of this same tape is over wrapped at a 2.8 mmpitch in a left-hand (i.e., opposing direction of wrap) lay.

Next, all three of the filaments are laid across the mandrel such thatthe distance of the filament portion between the mandrel and the wirebend corresponds with the desired spacing between electrodes. The bendof the 4.3m stripped length, 320 cm overall length wire is positionedclosest to the mandrel. The bend of the 34 cm stripped length, 320 cmoverall length wire is placed 32 mm further from the mandrel than thefirst bend. Finally, the third bend of the 34 cm stripped length, 220 cmoverall length wire, is placed 47 cm further from the mandrel than thefirst bend. The free ends of all the filaments are spiraled together ina right-hand lay direction around the mandrel at least 10 turns, andthen tied as a group with at least 5 hitch knots.

Rotating the winding machine in a right-hand lay direction, thefiber/wire combinations are coiled onto the mandrel, taking care thatall wires lay flat without crossing or twisting throughout windingprocess, at a 0.49 mm pitch until the end of the 4.3 cm stripped portionreaches the mandrel. Coiling is continued at a 0.76 mm pitch until thebend of the first 34 cm stripped portion reaches the mandrel, then at1.03 mm pitch until the end of the first 34 cm stripped portion, then at1.29 mm pitch until the bend of the second 34 cm stripped portion, thenat 1.73 mm pitch until the end of the second 34 cm stripped portion, andfinally at 2.09 mm pitch until the entire coiled length is then greaterthan about 53 cm. The wire ends are temporarily taped down to preventuncoiling.

Next, at the distal end of the construction immediately adjacent to thefirst-created electrode of the multi-filar coiled wire construction (theconstruction having been started with the distal end and progressing tothe proximal end), a circumferential wrap (i.e., not helical) of a 3.2mm wide tape is applied, using the previously described substantiallyimpermeable ePTFE/FEP insulating tape, until a lead diameter of 1.50 mmis achieved.

The electrode segment nearest the distal end (comprising the uninsulatedwire resulting from the 4.3 cm stripped wire length), that is, thesensing electrode, is then circumferentially wrapped with two or threelayers of a 3.20 mm wide tape that had been slit from a carbon-loadedePTFE film. This carbon-loaded ePTFE film has a density of about 0.4g/cc, is about 0.13 mm thick with about 25% ketchum-black carbon loadingby weight and an visually-estimated mean fibril length of about 10microns (from scanning electron photomicrographs of the film surface).Carbon-loaded ePTFE films may be made as taught by U.S. Pat. No.4,985,296 to Mortimer.

Next, an ePTFE film that has been coated with a layer of the previouslydescribed thermoplastic fluoroelastomer copolymer is obtained. The ePTFEfilm used is a film made as taught by U.S. Pat. No. 7,306,729 to Bacinoet al., having a thickness of less than about 0.0025 mm. With thefluoroelastomer coating, the composite film has a thickness of about0.028 mm. This film is slit into a 3.2 mm wide tape, six layers of whichis then circumferentially wrapped around the construct immediatelyadjacent to the proximal end of the sensing electrode (the first-createdelectrode made from the 4.3 cm length of uninsulated wire) with thefluoroelastomer side of the composite tape facing the surface of thelead. This wrapping forms a seal component that will separate theelectrode from the adjacent length of insulated portion of the lead andprevent the insulated portion from being contaminated with body fluids.

Using a 6.4 mm wide tape of the same composite ePTFE/fluoroelastomerfilm, five layers are applied as a circumferential wrap immediatelyadjacent to the proximal end of the second-created electrode (i.e., thedistal defibrillation electrode that was made from the first 34 cmlength of uninsulated wire). The same type of wrapping is appliedimmediately adjacent to both ends of the third-created electrode (i.e.,the proximal defibrillation electrode that was made from the second 34cm length of uninsulated wire).

A 0.76 mm wide carbon-filled ePTFE tape of the type described above iswrapped over the distal and proximal defibrillation electrodes, betweenthe seal components in order to fill the slight depression resultingfrom the uninsulated portion of the conductors used for the electrodes.

A 3.2 mm width of the carbon-filled ePTFE tape is helically wrapped witha 4.32 mm pitch in a right-hand lay over the proximal and distaldefibrillation electrodes between the seal components ensuring a tightbutt-joint with the seal components. A second wrap of this film isapplied over the first wrap in the same manner except with a 3.8 mmpitch applied with a left-hand lay.

Next, the entire length of the lead is helically wrapped with a 13.0 mmwidth of an ePTFE tape at a pitch of 4.3 mm. The film is the same filmdescribed above as taught by U.S. Pat. No. 7,306,729 to Bacino et al.,having a thickness of less than about 0.0025 mm.

Using a 3.2 mm width of the previously described substantiallyimpermeable ePTFE/FEP insulating tape, three layers arecircumferentially wrapped over the ePTFE/fluoroelastomer composite tapepreviously applied immediately adjacent to the proximal end of thesensing electrode, with the FEP side of the tape facing the surface ofthe lead. Next, a 6.4 mm width of this same ePTFE/FEP insulating tape iswrapped over the insulated lead portions (i.e., non-electrode portions)proximal to the proximal end of the distal defibrillation electrodeincluding over the seal components at a pitch of 3.7 mm. Finally, theentire construct is heated in a convection oven set at 320° C. for 3minutes.

After removing the construct from the oven and allowing it to cool toambient temperature, all ePTFE tape previously applied to the surface ofthe silver-plated copper wire mandrel that is exposed adjacent to thedistal end of the previously applied 1.5 mm diameter wrapping of thepreviously described substantially impermeable ePTFE/FEP insulating tape(located at the distal end of the construct) is removed by skiving.

A tubular housing, intended for use with the distal tip assembly andpacing electrode, is fabricated by cutting a 7.0 mm length of 0.064 mmwall thickness 304 or 316 stainless steel tubing having an insidediameter of 1.37 mm. This tubular housing is slid over the end of thesilver-plated copper wire mandrel along with a support coil temporarilyfitted inside of the tubular housing until the housing butts against the1.5 mm diameter wrapping of the insulating tape at the distal end of theconstruct.

Using a 6.4 mm width of the ePTFE/FEP insulating tape, a helical wrap isapplied (FEP-coated side facing the lead) beginning over the 1.5 mmdiameter wrapping of insulating tape and progressing distally over theend of the tubular housing. Next, a circumferential wrap of the sametape (also FEP-coated side facing the lead) is applied over the 1.5 mmdiameter wrapping of insulating tape and extending 3.2 mm over theproximal end of the tubular housing until a diameter of 1.7 mm isachieved.

The construct is then heated in an oven set at 320° C. for 4 minutes.After removal from the oven and cooling to ambient, the insulating tapeis trimmed from the distal transverse edge of the tubular housing andthe internal support coil is removed.

Next, the lead assembly is treated with a wetting agent. First, thecovered coil is soaked in isopropyl alcohol (IPA) at ambient temperature(about 21° C.) for 15 minutes. The covered coil is then immediatelytransferred to a solution of 2.0% polyvinyl alcohol (PVA) and de-ionizedwater and allowed to soak at ambient temperature for 70 minutes. Next,the covered coil is rinsed for 20 minutes in de-ionized water at ambienttemperature, after which it is soaked for 50 minutes in a solution of 2%gluteraldehyde, 1% hydrochloric acid (HCL) and de-ionized water, atambient temperature. Finally, the covered coil is rinsed in de-ionizedwater at ambient temperature for 2 hours and allowed to dry in ambientair.

After the wetting agent treatment, the resulting lead is removed fromthe silver-plated copper wire mandrel by applying appropriate tension tothe mandrel ends to cause the mandrel to elongate approximately 15 cm,resulting in sufficient necking of the mandrel to allow the lead toslide freely on the mandrel. Leaving the mandrel in place, a DF-4connector may be assembled onto the proximal end of the lead body. Asleeve support cap, first, and an insulating sleeve, second, are slidover the lead body from the proximal end toward the distal end. The wireends (2) of the first and second length segments for the sensingelectrode are pulled through the most proximal slot in the insulatingsleeve. The wire ends are then thermally stripped adjacent to theinsulating sleeve. A contact ring is slid on from the distal end of leadand over the sleeve support cap and onto the insulating sleeve andpressed over the sensing electrode wire ends with an interference fituntil flush with proximal end of insulating sleeve. An isolation ring isthen slid into place from the distal end of lead until it abuts theprevious ring contact. The distal defibrillation electrode wire ends arethen pulled through the middle slot, stripped and then another ringcontact and then another isolation ring are slid into place as describedabove. Next, the proximal defibrillation electrode wire ends are pulledthrough the distal slot, stripped and then a contact ring, followed byanother, longer isolation ring are slid into place as previouslydescribed. The pin connector bearing is pressed into proximal end ofinsulating sleeve. Protruding wire ends are trimmed adjacent to eachrespective proximal end of ring contacts and all rings are pressedtogether to close any gaps. Medical adhesive may be used to glueindividual parts together in assembly, and may also be used to backfillinside of the insulating sleeve. A strain relief sheath (preferably ofsilicone) is then slid over the distal end of the lead and onto thedistal end of the connector and attached with medical adhesive. With theadhesive dry, the multi-filar winding liner may be trimmed flush withthe pin connector bearing and the mandrel removed.

A 6-filar pacing coil is constructed using a 0.46 mm silver-platedcopper wire mandrel. Each filar is 0.076 mm 35NLT, 28% silver DFT wire(Fort Wayne Metals Corp., Ft. Wayne Ind.). Alternatively, multi-strandedwire may also be used. The 6 fillars are coiled onto the mandrel at apitch of 0.51 mm in the left-hand lay direction. Both ends of the coilare secured to the mandrel before cutting wires to keep the coil fromrelaxing into an increased diameter. The coil is then wrapped with an3.175 mm wide substantially impermeable ePTFE/FEP insulating tape at apitch of 2.85 mm (with the FEP-coated side facing the wire) and anotherwrap with the same tape in the opposite lay (also FEP down) at a pitchof 2.62 mm. The coil is then heated at 320° C. for approximately 4minutes. The pacing coil is removed from mandrel by stretching thesilver-plated copper wire until the coil is free to slide on mandrel andthen the ends are trimmed off to achieve the desired length.

A suitable fixation helix and post component is obtained; the helix ispreferably attached to the post by welding. A 0.51 mm diameter by 3.05mm long stainless steel wire is inserted into one end of pacing coiluntil flush with end. This end is inserted into the sleeve portion ofthe post/fixation helix assembly and crimped together, securing the postto the coil both mechanically and electrically. The pacing coilconductor is then inserted into the distal end of the previouslymanufactured lead. With the fixation helix located within the tubularhousing provided for the pacing electrode, a small cut and fold(adjacent edges of the cut are folded inward and caused to slightlyoverlap) is formed into the distal edge of the tubular housing, at onlyone point along the circumference of the distal edge of the tubularhousing. The cut and fold should be sufficient to serve as a guide toprevent the fixation helix from free-spinning without advancing.

A short length of 3.175 mm width of the previously describedsubstantially impermeable ePTFE/FEP insulating tape is attached with aheated iron (set at about 330° C.) parallel to outside of the tubulartip housing (FEP-coated side facing down) and pulled over open distaltip of housing and attached to opposite side of tubular tip housing. Thetape ends are trimmed at approximately the proximal end of tip housingand all edges are well-bonded with soldering iron. This is repeated fora total of two to five layers with each layer clocked at differentlocations around tip (i.e., radially disposed at about 72° intervals).Another length of this same tape is then applied helically (FEP-coatedside facing down) over entire length of the tip housing. A length ofFEP-coated porous ePTFE tape of about 6 mm width and a thickness of lessthan about 0.0025 mm is applied (FEP-coated side down) with one layerover the end of the housing and a helical layer around the housing in afashion similar to the previously-applied tape layers. This ePTFE tapeis generally made as taught by U.S. Pat. No. 5,476,589 to Bacino, andprovided with a discontinuous coating of FEP as taught by U.S. Pat. No.6,159,565 to Campbell et al. This layer is bonded by applying localizedconvection heat at 320° C. for a time sufficient to bond the film. Acoating of the previously described TFE/PMVE fluoroelastomer copolymercontaining dexamethasone sodium phosphate is spray-coated onto theexterior surface of the tip assembly sufficient to apply approximately 1mg of the steroid.

Torque is applied to the exposed proximal end of the pacing coilconductor sufficient to cause the fixation helix to rotate, extenddistally and pierce the film covering the distal end of the tubularhousing. Manual manipulation of the film may be required to aid thehelix in piercing the film. The fixation helix is then fully retractedinto the tubular tip housing (in the proximal direction, by rotating theproximal end of the pacing coil in the opposite direction). Next, theexposed proximal end of the pacing coil conductor may be trimmed to anappropriate length, after which the pin connector of a DF-4 connector isattached to the proximal end of the pacing coil conductor. This isaccomplished by first inserting a stainless steel tube (0.53 mm outsidediameter, 0.41 mm inside diameter and 5.6 mm length) into proximal endof pacing coil until flush. The tube and the proximal end of the pacingcoil are then inserted into the female socket of the pin connector untilthe pin connector is nested into the pin connector bearing and crimpedon proximal of connector flange. Finally, the retainer cap is fittedover the end of the pin connector and pressed into the pin connectorbearing.

An alternative manufacturing description is also provided that includesthe use of a helically wound noble wire applied around the circumferenceof a length of insulated wire to form an electrode. Other details arechanged as well while still other aspects remain the same. The aspectsthat remain the same are repeated in the following description toprovide continuity of the description.

First, a long length of wire for use as conductors 22, 24 and 26, suchas a 1×19 0.165 mm 35 NLT DFT (Ft. Wayne Metals Corp, Ft. Wayne, Ind.)stranded wire, is tape-wrapped with the previously describedsubstantially impermeable ePTFE/FEP insulating tape. The tape is ofabout 2.5 mm width and is applied with a pitch of about 2.5 mm with theFEP-coated side of the film facing away from the wire surface. Thetape-wrapped wire is heated to 320° C. for 20-45 seconds, i.e., a timesufficient to ensure that the construct is heated above the melt pointof the FEP. The wrapped wire is then wrapped again in the opposingdirection with a 3.3 mm wide tape of the same type at a pitch of 2.9 mmwith the FEP facing the wire surface. The wire is heated again above theFEP melt point.

The resulting insulated conductor wire, having a diameter ofapproximately 0.27 mm, is cut into two 320 cm lengths and one 220 cmlength. The integrity of the insulation may be tested at this time bysoaking the wires briefly in 100% isopropyl alcohol and then immediatelytransferring the wire to 9 g/liter saline. A suitable voltage source(e.g., a Quadtech Guardian 12KVDC Hipot Tester (Maynard Mass. 01754)) isconnected to both ends of each wire and 5 kV is applied for 15 seconds.Following testing the wires should be rinsed in de-ionized waterfollowed by a rinse in 100% isopropyl alcohol.

Next, the center portion of the length of each wire is stripped ofinsulation by suitable means (e.g., thermal stripping). The strippedlengths should be about 3 cm for one of the 320 cm samples and about 33cm for the other, and about 36 cm for the 220 cm long wire.

The stripped portion is then tape-wrapped with the previously describedthinner, substantially impermeable ePTFE/FEP insulating tape] of a slitwidth of about 2 mm resulting in an insulation thickness of about 0.01mm. Platinum/Iridium wire of about 0.05 mm diameter with then coiledover the thinly insulated section at a pitch of about 0.08 mm with thePt/Ir wire being passed across a metal surface heated to about 700° C.in close proximity to where it coils onto the thinly insulatedconductor. The temperature used is preferably above the melt point ofthe underlying thin conductor insulation. The Pt/Ir coil is held down onthe ends with a fluoroelastomer adhesive to prevent loosening ormovement of the coil. A 3.2 mm wide slit of the thin previouslydescribed substantially impermeable ePTFE/FEP insulating tape is wrappedradially around the center portion of the platinum-iridium coil with 2-4layers.

Each of these wires is then folded in half at the center of theplatinum-iridium coiled portion where the 3.2 mm insulation is, creatinga 180° bend at the center of the length of each wire. Finally, asufficient length of ePTFE filament appropriate to reach the distal endof the constructed lead when folded in half (further described below),of about 0.1 mm diameter, is looped around the apex of the bend of eachwire with a triple cableman's knot as shown in FIG. 3D.

Both ends of a length of silver-plated copper wire (intended to serve asa construction mandrel) are placed into the chucks of a winding machine.The wire mandrel will be used as a temporary substrate upon which willbe wound the multi-filar windings of the above-described conductors. Thediameter of the wire mandrel is chosen to be sufficient to provide thenecessary clearance to allow a pacing conductor coil to be rotated inthe lumen of the multi-filar winding so that the fixation memberelectrode, attached to the distal end of the pacing coil, may be screwedinto or removed from heart tissue. The wire mandrels for the followingmay be optimized to be the smallest practical diameter that allows forthe necessary pacing coil clearance in order that the outside diameterof the finished lead is minimal.

The silver-plated copper wire is then tape-wrapped with a thin ePTFEtape having a thickness of about 0.04 mm and of about 6.4 mm width, witha pitch of about 3.8 mm in a right-hand lay. Another layer of tape iswrapped over this first wrapping, using a 6.4 mm width tape of the sametype used for the wire insulating process described above, applied witha 3.6 mm pitch or alternatively the thinner substantially impermeableePTFE/FEP insulating tape described previously in a 6.4 mm width appliedat a pitch of 1.3 mm pitch. This layer is applied in a right-hand laywith the FEP-coated side of the film facing away from the surface of thesilver-plated copper wire. Next, a third layer is over wrapped with afluoroelastomer laminated to a thin ePTFE tape (same as first layer) ofa width of 3.2 mm at a pitch of 1.9 mm in a left hand lay with thefluoroelastomer facing away from the surface.

Next, all three of the filaments are laid across the mandrel such thatthe distance of the filament portion between the mandrel and the wirebend corresponds with the desired spacing between electrodes. The bendof the 3 cm stripped length, 320 cm overall length wire is positionedclosest to the mandrel. The bend of the 33 cm stripped length, 320 cmoverall length wire is placed 32 mm further from the mandrel than thefirst bend. Finally, the third bend of the 36 cm stripped length, 220 cmoverall length wire, is placed 45 cm further from the mandrel than thefirst bend. The free ends of all the filaments are spiraled together ina right-hand lay direction around the mandrel at least 10 turns, andthen tied as a group with at least 5 hitch knots.

Rotating the winding machine in a right-hand lay direction, thefiber/wire combinations are coiled onto the mandrel, taking care thatall wires lay flat without crossing or twisting throughout windingprocess, at a 0.76 mm pitch until the bend of the 33 cm portion is about1 cm from the mandrel. Coiling is continued at 1.29 mm pitch until thebend of the 36 cm portion is about 1 cm from the mandrel. Winding iscontinued at 2.09 mm pitch until the entire coiled length is thengreater than about 53 cm. The wire ends are taped down to preventuncoiling.

The SVC and RV electrodes are wrapped with 5-6 layers of 6.4 mm widetape that had been slit from a carbon-loaded ePTFE film in the oppositelay of the conductors. This carbon-loaded ePTFE film has a density ofabout 0.7 g/cc, is about 0.03 mm thick with about 27% ketchum-blackcarbon loading by weight. Carbon-loaded ePTFE films may be made astaught by U.S. Pat. No. 4,985,296 to Mortimer. The tape is cut parallelto the mandrel to create a 6.4 mm long taper of the thickness at eachend of SVC electrode and at the proximal end of the RV electrode. Thedistal end of the RV electrode is cut at about 103 degrees from themandrel on the distal side of the tape to achieve a 3.2 mm taper.

Next, at the distal end of the RV electrode, a 3.2 mm width of an ePTFEfilm that has been coated with a layer of the previously describedthermoplastic fluoroelastomer copolymer is obtained. The ePTFE film usedis a film made as taught by U.S. Pat. No. 7,306,729 to Bacino et al.,having a thickness of less than about 0.0025 mm. With thefluoroelastomer coating, the composite film has a thickness of about0.028 mm. This film is overlapped onto the carbon-loaded ePTFE filmabout 3.2 mm and wrapped with about 4 layers, the fluoroelastomer-coatedside facing inward, to the proximal end of the sensing electrode createdby the 3 cm stripped and coiled portion of the conductor. The film iscut parallel to the mandrel creating a 3.2 mm opposing taper with thecarbon-loaded ePTFE film on the proximal side and a 3.2 mm taperadjacent to the sensing electrode. A 3.2 mm width of the previouslydescribed carbon-loaded ePTFE is overlapped about 3.2 mm onto the distalend of the fluoroelastomer-coated ePTFE and wrapped with 5-6 layers tothe distal end of the sensing electrode. The film is cut perpendicularto the mandrel on the distal end.

Next, a 3.2 mm width of the previously described fluoroelastomer-coatedePTFE is wrapped circumferentially directly distal to the bend of thesensing electrode adjacent to the carbon-loaded ePTFE with about 8layers. This is then over-wrapped circumferentially with 6.4 mm widepreviously described thinner, substantially impermeable ePTFE/FEPinsulating tape with FEP-side facing inward. About 5 layers are appliedoverlapping the carbon-loaded ePTFE film over the sensing electrode byabout 1 mm. The fluoroelastomer-coated ePTFE portion between the sensingand RV electrodes is over-wrapped with the previously described thinner,substantially impermeable ePTFE/FEP insulating tape of a width of 3.2 mmFEP-side facing inward with about 5 layers overlapping equally onto thecarbon-loaded ePTFE of the sensing and RV electrodes.

A 6.4 mm width of the previously described fluoroelastomer-coated ePTFEis wrapped with fluoroelastomer facing inward with about 4 layersbetween the SVC and RV electrodes and proximal of the SVC electrode forabout 25 cm in the opposite lay of the conductors (same lay as thecarbon-loaded ePTFE). For greater abrasion-resistance and increasedrobustness of the lead body proximal of the SVC electrode, the 4 layersof fluoroelastomer-coated ePTFE may be transitioned into 6 layers bydecreasing the wrapping pitch at a desired distance, (e.g., 3 cm)proximal of the SVC electrode.

The film is cut into a tape with parallel edges and overlapped about 6.4mm onto the carbon-loaded ePTFE at each end of the SVC electrode and theproximal end of the distal electrode to create the opposing taper. Theseportions are then over-wrapped with the previously described thinner,substantially impermeable ePTFE/FEP insulating tape, FEP inward, withabout 5 layers overlapping onto the carbon-loaded ePTFE about 1 mm oneach end of the SVC electrode and the proximal end of the RV electrode.A 0.0025 mm thick, 6.4 mm wide, porous ePTFE tape, made as taught byU.S. Pat. No. 5,476,589 to Bacino, and provided with a discontinuouscoating of FEP as taught by U.S. Pat. No. 6,159,565 to Campbell et al.,is overwrapped over the previous layer at the proximal end for about 3.5cm and about 4 layers with FEP-inward to improve adhesion of thesilicone strain relief of the IS-4 connector described later.

Clamps with a through hole of about 1.65 mm may be applied over thelocation of each bend to prevent movement of the bends during cooking. Abend may also placed in the distal end of the lead and mandrel prior tocooking resulting in a set curve in the final lead on the distal end.The entire construct is heated in a convection oven set at 320° C. for15 minutes.

After removing the construct from the oven and allowing it to cool toambient temperature, all ePTFE tape previously applied to the surface ofthe wire mandrel that is exposed adjacent to the distal end of thepreviously applied 3.2 mm circumferentially wrappedfluoroelastomer-coated film (located at the distal end of the construct)is removed by skiving.

A tubular housing, intended for use with the distal tip assembly andpacing electrode, is fabricated by cutting a 7.0 mm length of 0.064 mmwall thickness 304 or 316 stainless steel tubing having an insidediameter of 1.37 mm. This tubing may be laser cut to include a featurethat can be bent into the lumen providing a thread guide as describedpreviously. The housing may also include a PTFE bushing in the proximalend to support the helix assembly during extension and retraction. Thistubular housing is slid over the end of the silver-plated copper wiremandrel along with a support coil temporarily fitted inside of thetubular housing and PTFE bushing until the housing butts against theskived edge at the distal end of the construct.

Using a 6.4 mm width of the ePTFE/FEP insulating tape, a helical wrap isapplied (FEP-coated side facing inward) beginning over the thinner,substantially impermeable ePTFE/FEP insulating tape at the distal end ofthe carbon-loaded ePTFE film of the sensing electrode and progressingdistally over the end of the tubular housing applying about 5 layers.The same film is then wrapped back in the opposite direction over thesame portion with the same number of layers. Next, a circumferentialwrap of the same tape the previously described fluoroelastomer/ePTFElaminate film (fluoroelastomer-inward) is applied at the proximal end ofthe tubular housing and adjacent to the carbon-loaded ePTFE film of thesensing electrode until a diameter of 1.63 mm is achieved. Next, 5layers of 6.4 mm previously described thinner, substantially impermeableePTFE/FEP insulating tape is wrapped circumferentially (FEP side facingdown or inwardly) over the previous fluoroelastomer/ePTFEcircumferential wrap. Additionally, a 0.0025 mm thick, 6.4 mm wide,porous ePTFE tape, made as taught by U.S. Pat. No. 5,476,589 to Bacino,and provided with a discontinuous coating of FEP as taught by U.S. Pat.No. 6,159,565 to Campbell et al., may be applied circumferentially (FEPside facing down or inwardly) with about 2-3 layers over the distal endof the tubular housing to allow for adhesion of drug-eluting layersand/or tip flange features.

The curve on the distal end is reformed, if applicable, and theconstruct is then heated in an oven set at 320° C. for 5 minutes. Afterremoval from the oven and cooling to ambient, the insulating tape istrimmed from the distal transverse edge of the tubular housing and theinternal support coil is removed.

The clamps over the bends are also removed. The carbon-loaded ePTFE filmis then densified against a heated rod at 365 ° C. by spinning theconstruct at about 1000 rpm and traversing at 12.7 cm/min with a pass ineach direction.

The IS-4 connector is made using 3 contact rings with legs. Contactrings are laser-cut from a stainless steel tube of an OD of 3.2 mm andan ID of 2.7 mm. Each leg is cut about 0.3 mm wide. The sensing contactleg is 0.16.3 mm long, the distal contact leg is 11.8 mm long, and theproximal contact leg is 7.2 mm long. Each leg is bent inward at thejunction with the ring portion of the contact and bent in the oppositedirection about 1 mm from the ring so that the leg becomes parallel withthe axis of the ring. The created jog brings the leg about 0.7 mminward. The leg of each contact is inserted into a stainless steel tube(0.53 mm outside diameter, 0.41 mm inside diameter and 7.6 mm length)about 3.8 mm and the tube is crimped in place. Each contact is assembledover an inner tub (1×72 UNF Thread OD and 1.1 mm ID) with the leg of thesensing contact passing through both the distal and proximal contact,and the distal contact passing through the proximal contact. Each leg isspaced about 120 degrees apart axially. Each contact is spaced apartaccording to published IS-4 specifications and the threaded tube ispositioned approximately aligned with the open end of the tube on thecontact legs and protruding beyond the edge of the sensing contact theappropriate depth given the hole and shoulder on the IS-4 cap. Theappropriate depth should accommodate the flange on the connector pinallowing it to be trapped between the inner tube and the IS-4 capallowing for rotation with limited axial movement when the IS-4 cap isfully seated into the sensing contact. The cap and connector pin aredescribed further later. The contacts and inner tube are over-moldedwith a high-durometer silicone, epoxy, or polyurethane providing asmooth transition from the molded face to the OD of the contacts.Appropriate molding techniques are employed to reduce air bubbles andimprove adhesion to contacts and inner tube. Approximately 2.5 mm of theopen ends of the tubes crimped to the contact legs are left exposed atthe distal end of the molded connector.

A portion of the conductors off the end of the wrapped portion of thelead construct are unwound to expose a portion of the inner-wrappedlayers at least as long as the IS-4 inner tube. This is preferably donebefore the silver-plated copper wire mandrel is necked and removed. TheIS-4 connector is slide over these film layers adjacent to the helicallywound conductors. The insulation of each conductor is stripped away nearwhere is leaves the helically winding. Each conductor is cut at theappropriate length and inserted into the corresponding tube on the IS-4connector with two stripped conductors inserted into each tube. The tubeis crimped to secure the conductors both mechanically and electrically.A silicone strain relief is then over-molded over the distal end of theIS-4 where these connections are made and extends onto the lead body. Apre-molded strain relief may also be used and attached with siliconemedical adhesive filling the area where these connections are made in acounter-bore of the strain relief and also adhering the strain relief tothe lead body and IS-4 connector.

Once silicone is properly cured, the resulting lead is removed from thesilver-plated copper wire mandrel by applying appropriate tension to themandrel ends to cause the mandrel to elongate approximately 15 cm,resulting in sufficient necking of the mandrel to allow the lead toslide freely off the mandrel.

A 6-filar pacing coil is constructed using a 0.46 mm silver-platedcopper wire mandrel. Each filar is 0.076 mm 35NLT, 28% silver DFT wire(Fort Wayne Metals Corp., Ft. Wayne Ind.). Alternatively, multi-strandedwire may also be used. The 6 filars are coiled onto the mandrel at apitch of 0.51 mm in the left-hand lay direction. Both ends of the coilare secured to the mandrel before cutting wires to keep the coil fromrelaxing into an increased diameter. The coil is then wrapped with an6.4 mm wide of the thinner, substantially impermeable ePTFE/FEPinsulating tape insulating tape with about 5 layers (with the FEP-coatedside facing the wire) and another wrap with the same tape in theopposite lay (also with the FEP-coated side facing the wire) with anadditional 5 layers. The coil is then heated at 320° C. forapproximately 5 minutes. The pacing coil is removed from mandrel bystretching the silver-plated copper wire until the coil is free to slideon mandrel and then the ends are trimmed off to achieve the desiredlength.

A stainless steel tube (0.53 mm outside diameter, 0.41 mm insidediameter and 7.6 mm length) is inserted into proximal end of pacing coiluntil nearly flush. The pacing coil is inserted into the lumen of thelead body. The tube and the proximal end of the pacing coil are theninserted into the female socket of the pin connector until fully seatedand the pin connector is flush with the inner tube of the IS-4connector. The pacing coil is then trimmed flush with the tip housingand then an additional 3.7 mm is trimmed from the same end. A suitablefixation helix and post component is obtained. A 0.51 mm diameter by3.05 mm long stainless steel wire is inserted into the tip end of pacingcoil until flush with end. This end is inserted into the sleeve portionof the post/fixation helix assembly and crimped together, securing thepost to the coil both mechanically and electrically. The pacing coilconductor is then inserted into the distal end tip housing of thepreviously manufactured lead. With the fixation helix located within thetubular housing provided for the pacing electrode, the tab feature, ifapplicable, on the tip housing is bent inward to create the threadguide. The fixation helix should extend and retract easily (within 3-10rotations of the pacing coil from the proximal end of the leadassembly).

The fixation helix is then fully retracted into the tubular tip housing(in the proximal direction, by rotating the proximal end of the pacingcoil in the opposite direction). The pin connector is nested onto thepacing coil adjacent to the IS-4 inner tube and crimped on proximal ofpin connector flange. Finally, the IS-4 cap is placed over the pinconnector and threaded onto the IS-4 inner tube until fully seated intosensing contact and sealed with silicone or epoxy adhesive.

A porous ePTFE is wrapped over the end of a 1.6 mm construction mandreland then radially wrapped 6.4 mm wide by 22 mm long tape of porous ePTFEpreviously coated with the previously described TFE/PMVE fluoroelastomercopolymer containing approximately 1 mg of dexamethasone sodiumphosphate with the wraps held in place with a fluoropolymer adhesivethat may also contain dexamethasone sodium phosphate. The drug-loadedfilm tube is then removed from the construction mandrel and slid ontothe tubular housing on the distal tip of the lead that was previouslycovered with porous ePTFE/FEP tape and attached with the fluoropolymeradhesive. The drug loaded film tube may also include flange-likefeatures as previously described to allow for a more atraumatic tip.

Torque is applied to the pin connector sufficient to cause the fixationhelix to rotate, extend distally and pierce the film covering overdistal end of the tubular housing. Manual manipulation of the film maybe required to aid the helix in piercing the film.

The lead of the present invention has good fatigue resistance. Leads of5 French diameter were manufactured in accordance with the secondmanufacturing description presented above. These leads were tested in acyclic 180 degree bending test as will be further described (plus andminus 90 degrees) through a radius of curvature of 6 mm wherein all fivesamples tested of the present lead survived in excess of 3,000,000cycles without failure (i.e., they survived more than 100,000 cycles,more than 250,000 cycles, more than 500, 000 cycles, more than 1,000,000cycles, more than 1,500,000 cycles, more than 2.000,000 cycles, morethan 2,500,000 cycles). All samples tested (all of which included pacingcoils) of a commercially available lead in this test failed atconsiderably fewer cycles. Failure was identified as a significantincrease in electrical resistance of the test sample and confirmed bypresence of a visible fracture in any conductor.

The inventive leads also excelled in a comparative test for abrasionresistance as described below.

Flex testing (a bending fatigue test) and abrasion testing wereperformed on samples of the inventive leads built according to thesecond of the above manufacturing descriptions. Commercially availableleads were also tested as controls.

Flex testing was conducted in the following manner.

A test fixture was constructed in accordance with the FIG. 106 ofCENELEC test standard 45502-2-2:2008, section 23.5, with the exceptionthat the fixture radius was 2.17 mm.

The bending radius along the longitudinal centerline of any lead undertest varied as a function of the diameter of the test sample.

The test machine was constructed such that the fixture alternatelyoscillated 90+0/−5 degrees both sides from vertical and the test sampleflexed in the bell mouth of the fixture, in accordance with theabove-mentioned test standard.

A load of 235 g was used, and in accordance with the above-mentionedtest standard was sufficient to assure that the centerline of the testsegment conformed to the bending radius was attached to the lower end ofa thin, flexible PTFE line strung through the test segment so that itconformed to the bending radius.

The oscillating rate was set at 4 Hz.

Samples were subjected to EtO sterilization (54 deg C., total cycle timeof about 15 hours). Commercially available test samples had beensterilized by the manufacturer and, therefore, were not subjected to anadditional sterilization cycle.

All flex-tested lead body samples were taken from lead body portionsproximal of the SVC electrode. Individual test samples were taken fromsingle leads.

An electrical connector was attached to all conductors at each end ofthe sample; the two connectors from the two sample ends were thenconnected to an ohmmeter. A sample was deemed to have failed upon a 0.02Ohm increase in resistance. Visual inspection was then performed toverify fracture of one or more conductors. Five samples of each sampletype were tested.

Flex testing was performed on samples of the inventive lead builtaccording to the second of the above provided manufacturingdescriptions, as well on ENDOTAK RELIANCE® G ICD leads (Model 0185 L,Boston Scientific, Natick, Mass.). The ENDOTAK RELIANCE leads werechosen as the basis for comparison as they appear to have the bestclinical history for longest implant life in the industry at present.Samples of the present invention all exceeded 3 million cycles withoutfailure; ENDOTAK RELIANCE lead samples all failed prior to 300,000cycles. Note that the ENDOTAK RELIANCE lead samples are of asymmetrictransverse cross section while the inventive test lead samples were allof symmetric transverse cross section whereby sample orientation did notmatter. Consequently, three of the ENDOTAK RELIANCE lead samples wereoriented in one direction while the other two were oriented at 90degrees with respect to the orientation of the first three. Test resultsare presented in Table 1; orientation of the ENDOTAK RELIANCE leads inthe bending fixture is indicated in the table where the adjacentvertical left and right lines shown in the table represent the bendingsurfaces.

TABLE 1 Cycles to end of Conductor Sample test Failure OrientationInventive 3,396,044 no n/a Inventive 3,389,961 no n/a Inventive3,390,601 no n/a Inventive 3,383,701 no n/a Inventive 3,344,911 no n/aENDOTAK 99,775 yes

ENDOTAK 75,892 yes

ENDOTAK 109,633 yes

ENDOTAK 299,802 yes

ENDOTAK 276,186 yes

Abrasion testing was performed as follows.

First, an ICD lead abrasion tester was constructed in the followingmanner, as shown generally by the schematic side view of FIG. 23.

An aluminum arm 402 (14 cm long, 2 cm wide, 0.5 cm thick) was fabricatedand a titanium blade 404 was attached by screws to one end of arm 402.Blade 404 was 2.5 cm high, 1.5 cm wide and 1.59 mm thick. One end of theblade was shaped to a full radius of 0.795 mm in order to simulate thesmallest edge of a typical ICD generator. The blade 404 was attached toarm 402 such the flat end was flush with the arm and the lower end ofblade 404 extended about 0.5 cm below arm 402.

The other end of the arm was connected to the crankpin 406 of a circularplate 408 that served as a crankshaft. The center of circular plate 408was attached to a shaft 410 of an electric motor (not shown) such thatrotation of circular plate 408 by the electric motor caused blade 402 totranslate back and forth as indicated by arrow 412. The rotation speedand translation distance (stroke length) were set to 96 revolutions/minand 1.3 cm, respectively.

An aluminum block 414 (2.5 cm long, 3.0 cm wide, 2.0 cm thick) wasobtained. A groove was cut into the 2.5 cm by 3.0 cm upper surface ofthe block along the middle of the 2.5 cm length, in order to providesupport for and to center the lead sample. The upper surface of block414 was centered to the movement of the blade.

Two clamps 416 were provided on a stationary platform to hold a leadsample 418 fixed in position.

Weights 419 in the form of metal washers were placed on top of aluminumarm 402 to ensure contact between the blade and the test sample. A forcegauge (Ametek Accuforce III, Largo Fla. 33773) was temporarily attachedto the lower, radiused edge of blade 404. Washers were added until theforce required to raise the arm reached 285 g.

A 24 volt power source was obtained, one pole 420 of which was connectedto all of the conductors of the test sample. The other pole of the powersource was connected to the rotating circular plate 408, which was inelectrical contact with arm 402 and blade 404.

A proximity sensor was located adjacent to the aluminum arm and was usedto detect the number of back and forth translations of the blade. Theoutput of the detector was connected to a counter. Each back and forthtranslation of the blade was counted as a single cycle (i.e., one fullrevolution of circular plate 408). The counting circuit included anelectrical feedback loop that was designed such that the test wasstopped once electrical contact was made between the blade and the testsample conductor(s) (i.e., failure occurred). That is, the circuit wascompleted due to blade 404 making electrical contact with any of theouter conductors of test lead 418 as a result of abrasion through theinsulation on the conductors.

Electrical contact was defined as a resistance reading through the bladeto the lead body conductor of less than or equal to 3300 ohms. In allcases, electrical contact between the blade and the lead occurred onceany of the outer conductors of the lead 418 were visibly exposed.

Test samples were prepared in the following manner.

Samples were subjected to EtO sterilization (54 degrees C., total cycletime of about 15 hours). Commercially available test samples had beensterilized by the manufacturer and, therefore, were not subjected to anadditional sterilization cycle.

All abrasion-tested lead body samples were taken from lead body portionsproximal to the electrodes. Individual test samples were taken fromsingle leads.

An electrical connector was attached to all conductors at one end of thetest sample; the connector was then connected to pole 420.

Testing was conducted as follows.

A 1.5 cm portion of the test sample was positioned inside the grooves ofthe block face, under the blade. The sample was fixed in position bysecuring both ends with the clamps attached to the stationary platform.

The test was initiated and continued until failure occurred.

Samples were tested and the values for the cycles to failure are shownin Table 2. Abrasion testing was performed on additional samples of theENDOTAK RELIANCE® G ICD leads described above with regard to flextesting. Abrasion testing was also performed on the RIATA® ST Optim™Defibrillation lead, Model 7022 (St. Jude Medical, St. Paul Minn.). TheRIATA ST Optim lead was chosen because of its small diameter andreported abrasion resistance. It is noted that the ENDOTAK RELIANCE leadsamples are of asymmetric transverse cross section as describedpreviously. The inventive test lead samples were all of symmetrictransverse cross section while the RIATA ST Optim are substantiallysymmetrical in transverse cross section, consisting of a central pacingcoil centered along the longitudinal axis of the lead and additionallyhaving three pairs of conductors extending along the length of the leadwith the three pairs spaced radially apart 120 degrees with insulatingmaterial of the lead body between each of the three pairs. The threepairs of conductors are located closer to the outer surface of the leadbody than the pacing coil. Abrasion test results of the RIATA lead maytherefore vary as a function of whether the blade 404 of the tester issubstantially centered above a pair of conductors or alternatively issubstantially centered above the insulating material between adjacentconductor pairs. The RIATA lead orientations were chosen at random whilethe ENDOTAK leads were oriented so that the portion of the pacing coilclosest to the surface of the lead body was located closest to blade404.

Both the 4-layer and 6-layer fluoroelastomer-coated ePTFE inventivesamples were made as described in the second manufacturing descriptionprovided above.

TABLE 2 Cycles to Lead Type Failure ENDOTAK  3,625 ENDOTAK  1,513ENDOTAK  2,137 ENDOTAK  2,366 ENDOTAK  2,374 RIATA  73,225 RIATA  31,407RIATA  5,143 Inventive 4-Layer  12,225 Inventive 4-Layer  14,531Inventive 4-Layer  14,783 Inventive 4-Layer  17,284 Inventive 4-Layer 33,581 Inventive 6-Layer 100,375 Inventive 6-Layer  85,565 Inventive6-Layer  71,374

In addition to being directed to the embodiments described above andclaimed below, the present invention is further directed to embodimentshaving different combinations of the features described above andclaimed below. As such, the invention is also directed to otherembodiments having any other possible combination of the dependentfeatures claimed below.

Numerous characteristics and advantages of the present invention havebeen set forth in the preceding description, including preferred andalternate embodiments together with details of the structure andfunction of the invention. The disclosure is intended as illustrativeonly and as such is not intended to be exhaustive. It will be evident tothose skilled in the art that various modifications may be made,especially in matters of structure, materials, elements, components,shape, size and arrangement of parts within the principals of theinvention, to the full extent indicated by the broad, general meaning ofthe terms in which the appended claims are expressed. To the extent thatthese various modifications do not depart from the spirit and scope ofthe appended claims, they are intended to be encompassed therein.

We claim:
 1. An electrode for an implantable lead comprising a length ofa first electrically conductive wire provided with an outer insulatingcovering, said covered first wire being further provided with a lengthof a second, uninsulated, electrically conductive wire helically woundtightly around the outer insulating covering of said first wire suchthat said first and second wires are in electrical communication.
 2. Anelectrode according to claim 1 wherein said first and second wires areof dissimilar metals.
 3. An electrode according to claim 2 wherein saidsecond wire is a noble metal.
 4. An electrode according to claim 3wherein said second wire comprises platinum.
 5. An electrode accordingto claim 3 wherein said second wire comprises an alloy of platinum andiridium.
 6. An electrode according to claim 1 wherein said first wire isa multiply stranded wire.
 7. An electrode according to claim 1 whereinsaid second wire is a solid wire.
 8. An electrode according to claim 1wherein said electrode is provided with an outer covering of aconductive polymeric material over said first and second wires.
 9. Anelectrode according to claim 8 wherein said conductive polymer is afluoropolymer.
 10. An electrode according to claim 9 wherein saidconductive polymer comprises expanded polytetrafluoroethylene havingvoid spaces containing carbon.
 11. An electrode according to claim 1wherein said insulating covering is a fluoropolymer.
 12. An electrodeaccording to claim 11 wherein said fluoropolymer comprisespolytetrafluoroethylene.
 13. An electrode according to claim 11 whereinsaid fluoropolymer comprises polytetrafluoroethylene and fluorinatedpolypropylene.
 14. An electrode according to claim 1 wherein said firstwire is a stranded wire with strands laid up at a first pitch and saidsecond wire is a solid wire helically wound at a second pitch that isfiner than said first pitch.